AweSIM

Hi,

I recently purchased a ZWO ASI294MC Pro and was very happy with the results till a few days ago when all my processed images started turning up horrible. I've narrowed the problem to calibration frames not being correct. I've listed all problems with the calibration frames in this post, in hopes someone here can help me sort them out:

PS. For all frames, I kept the camera temperature at 0C, gain and offset at 10. (And while we're at it, what gain/offset values do you guys use and why? Is it just a personal preference or is there a way to determine what gain/offset should I use? Does it depend on target, visibility conditions, narrowband filters, etc?)

Also, I used the following exposure times for different calibration frames: BIAS (0s), DARKS (300s), FLATS (5s), LIGHTS (300s), DARK FLATS (5s).

Also, the frames were captured in SGP and processed in PI.

1. The bias frames are wierd, to say the least. Being a DSLR user till recently, I'm used to seeing the raw, bayered, stretched BIAS frame to be an image full of random noise with no discernible patterns. When I look at the ZWO ASI294MC Pro's BIAS frames, and stretch it, I can see the bayer grid pattern very clearly. The GREEN pixels have the lowest brightness while the BLUE pixels have the highest brightness. I took BIAS frames by detaching the camera from the OTA and putting its cap back on and turning off all lights in the room (to ensure no stray light leaked in).In the first attachment, you can see auto-stretched image of a BIAS i took with my earlier NIKON. The image is bayered but still the noise is random. In the same image, you can also see the auto-stretched image of the BIAS i took with ASI294. The bayer pattern is clearly visible. If I split the CFA based on each CFA channel (1, 2, 3, 4), and auto-stretch them, the noise is random. However, the clearly different bias of each channel in the CFA raw file is what's bothering me. I haven't been able to find samples of a BIAS frame online taken from this camera, so I'm hoping that someone here with the same camera can tell me what I'm doing or understanding wrong here.

2. I took 20 darks of 5m each. The uncalibrated DARKS show the same bayer pattern and auto-stretch barely shows any amp glow. However, when I calibrate them against the MASTER_BIAS and integrate them into a MASTER_DARK, and look at it after auto-stretching, I can see no bayer pattern and the amp glow is clearly visible. This tells me that what I'm doing is right so far. However, when I calibrate flat frames against the MASTER_BIAS and MASTER_DARK and integrate them, I see a grainy result that shows the vignetting clearly but the amp glow is visible as a dark patch in one corner. This is wrong, I think. The exact steps I'm doing are listed in the guide that I'm following: https://www.lightvortexastronomy.com/tutorial-pre-processing-calibrating-and-stacking-images-in-pixinsight.html

If it helps, I've uploaded 5 files of each type of frame (due to space constraints) on google drive that are available at https://drive.google.com/open?id=1fsxw_LIDH7B-DqJrN7WBXQQhOwB-ezKz if you want to take a closer look at the data. So far, I've tried a lot of combinations of settings in PI but haven't been able to find or come up with a workflow that reliably works for me. I would be really really really grateful if someone could help me out or point me in the right direction.

Finally, is it possible that I might've damaged the camera and that's why its not giving me good results now? I took superb images of the Orion and Rosette just days earlier and only now I am facing these issues. I lost raw frames for those targets so I cannot compare BIAS/DARKS of those images. I haven't dropped the camera, haven't gotten it wet (except when its cold and dew forms outside the casing. I cool it down via SGP down to 0C from 10C in about 4-5 mins. When warming it up, I sometimes ask SGP to warm it up to 15C in 5 mins but most of the time just stop the cooling aid so it warms up by itself. Is that the right way or a recipe for a disaster already happened or waiting to happen?

Thanks,

A very anxious member who's dreading something's massively wrong with his very expensive gear that he cannot afford again. =(

Asim

On 20/01/2020 at 04:18, John said:

Hello Asim.

I have just had a look at the internal componants of my 9x50 right angled correct image Skywatcher finder eyepiece and it seems to be the same as your arrangement A.

Having put mine back together the finder works fine. I think the eyepiece of your 9x50 should be a similar design ?. I think the only difference with the RACI finder is the prism diagonal and the shorter finderscope body.

Perhaps try that configuration again ?

Maybe the objective of your finder has shifted as well ?. Worth checking at least.

Edit: also worth checking that the lenses and spacers in the eyepiece have seated properly - it can be a bit tricky to get them all in a neat stack so that they go back into the eyepiece body neatly and properly seated.

 

Hi John. Thank you so much for your response. I'll try that configuration again and let you know how it goes. Your point regarding seating of the elements is a good point. I'll double check that too. I'll also try to post an image of what the finderscope shows.

Thanks. 🙂

Hi,

I have a SkyWatcher 9x50 finderscope that came with my SkyWatcher 200 DS OTA. The other day, I was disassembling the eyepiece of the finderscope to clean its lenses and I kind of messed up. When I unscrewed the crosshair retainer ring, I flipped it over to pop out the lens, expecting it to have only a single lens. Contrary to my expectations, two lenses and two spacers popped out. Since it happened very quickly, I don't know the order these lenses are supposed to go back. Although I have tried assembling back a couple of possible combinations of these elements, I am unable to properly focus my finderscope.

The eyepiece of the finderscope has the following elements inside it:

1. A retainer ring with crosshair stretched across it with a screw thread to lock everything in place. I know this is the last element in the assembly. I'll denote this with [ # ].

2. A small spacer (maybe 2mm), denoted by [ = ]

3. A large spacer (maybe 10mm), denoted by [ === ]

4. Two double-element lenses with one side flat and the other side convex, denoted by [ |) ]

I've tried the following combinations without success:

A. [ #  ===  |)  =  (| ]

B. [ #  ===  (|  =  |) ]

C. [ # . ===  = (|  |) ]

But none of these combinations are working. I remember how much I had to screw the objective lens in or out to reach visual focus for the finderscope, but now the focus is occurring near or just outside the limits of the primary lens threads. Also, the view through the finderscope show strange halos which aren't centered.

I'm hoping that someone here might possess the same finderscope and can tell me what order do these elements go inside the eyepiece assembly.

Thanks a lot!

Asim

On 02/12/2019 at 13:27, wimvb said:

Have you checked the ZWO site? 

Assuming the coma corrector has 55 mm backfocus, like this

https://www.firstlightoptics.com/coma-correctors/skywatcher-coma-corrector.html

Just make sure the threads match (M42, M48) 

Hi! Thanks a lot for that information mate! I had thought that I would've needed to buy extra extension rings or adapters. But you're right, the camera itself comes with all the required accessories. That is impressive. 🙂

Any advice from anyone here? 🙂

Hi,

I have a SkyWatcher 200 PDS OTA and a Nikon D90 camera for imaging. A friend of mine is coming to Pakistan from Australia and I'm planning to have him purchase and bring over some gear for me.

I'm ordering a SkyWatcher Coma Corrector for F5 scopesscopes, and perhaps a ZWO ASI294MC ProPro camera as well.

I want to ensure that when he comes, I will have everything I need and not some missing items. In particular, I'm worried about back focus distances and spacers required.

I want to ensure that I be able to use both my D90 and ASI294 MC Pro with the coma corrector. But I'm not sure what spacers I will need.

The coma corrector manual states it requires a back focus distance of 55mm.

The ZWO manual states it has a back focus distance of 6.5mm with the 11mm T2 extender taken off. There are some spacers included in the package but I'm not sure what they are for and if they will fit my setup as I'm not really well versed in the science of thread types.

I don't know what is the back focus distance of D90.

Can you guys please help me identify what adapters and spacers I'll need to ensure that both my D90 and ZWO can be coupled to my scope?

Since we don't have any astronomy shops in Pakistan, and my friends don't come frequently from abroad, I want to avoid the situation where I have the cameras and the coma corrector but can't use it since I don't have the proper spacers or adapters.

Thanks and best regards,

Asim Sohail

Pakistan

6 hours ago, Erling G-P said:

I have the same scope as you, and am using Skywatcher's 0.9 reducer/CC.  I have never used the scope for imaging without it, so can't offer any with/without comparisons.  One advantage of this CC is that it will work with other scopes too - a 130PDS for example.  Got such one a couple of months ago, for wider field work, but regrettably weather hasn't permitted me to use it even once yet.

Below are some shots with the 200PDS, on an unguided HEQ5Pro, using a Nikon D7000, with 30-sec exposures stacked, so a setup very similar to your own:

 

Hi Earling!

Thanks a lot for sharing those images. Seeing that you have the same setup as myself, the images you shared are so much insightful! Just recently, I managed to go to a dark sky site and had the chance to photograph the Andromeda myself. I was constrained on time so took 5 minute stacks of 30s exposures each and there's a good chance my focus wasn't perfect as I bring my Bahnitov mask along. I've shared my final stack below. I can immediately see a few things:

1. The coma in my pic is noticeable clearly even though I haven't cropped any part of the frame. In your pic, I cannot see any coma and certainly not even close to what I have in my stack.
2. Your image processing skills are way better than mine as I've blown the core of Andromeda and you've managed to keep it intact.

To me, #1 is a clear indication that I NEED to be get my hands on a Coma Corrector now. It should get me much better stars across the field. Even then, I have a lot more to learn. Can you share how long your Andromeda stack was? When you say "unguided", I'm assuming you meant tracked but not auto-guided. At the moment, I'm also thinking about getting an auto-guider setup for myself. Seeing how better your pics are than mine, I'm getting doubtful if I'm overspending and that I simply need to get a CC and not invest in an guider scope/camera and a dedicated astronomy camera. What would your thoughts be about it?

I live under VERY light-polluted urban skies, so much so that my city images suffer from a massive pink/brown overcast. What sort of skies did you take these images of yours? If you live under as light-polluted skies, then that's a reason for me to stop doubting my equipment and work on my skills, instead of investing in a dedicated cooled camera and auto-guider setup and narrow-band filters to allow me to cut light pollution and be able to take longer, tracked exposures that will allow me to see more detail in my images.

19 hours ago, joe aguiar said:

ill give you my opionion

I have never owned or  used coma corrector on any scopes, even on my F/4.5 dob.

saying that tho you have an f/5 system so its gonna have that its standard so for visual it never bothered me in the slightest. Your pic is I think decent however your 2nd pic blown up does show it BUT it only cause its soo blown up tho. many people buy f/4 reflectors for imaging so it will even be worse in those but at f/5 I think image is ok

I guess the issue tho comes cause you want to do imaging so that's a whole different ball game. almost every scope that people buy for imaging will need a focal reducer or like your coma corrector or flate field. this is part of getting into this part of the hobby. There are some scopes that don't need these extra accessiors BUT cause they have those items built into it. The price is more expensive tho.

you are correct coma corrector are expensive even the badder ones are so expensive that I wouldn't even get one here where iam the badder one is $285 +49 shipping then tax that's $377.42. yet that's the cost pretty much of the whole ota tube.

To me as I said in another post I would never buy an accessiory that costs as much as the scope itself,cept maybe eyepices where they can be used on every scope ( I own 11 or 12 scopes right now about) so that makes sence.

so I guess if you plan on imaging that's kinda what you need to do tho.

joejaguar

Hi! Thanks for your advice. Yes you're right. Whereas the coma is not problematic for visual work, but it is for imaging. The second image I uploaded was the same image but at 100% zoom. Since most galaxies and nebula appear quite small on the camera frame, I usually have to crop an image to allow more detail to be seen. This is where coma becomes a lot apparent. When I initially got my OTA, I didn't know that much about coma and I frankly didn't get it why would so many people settle for high quality, small aperture refractors when you could have an 8" newtonian for far less cost. But I have learnt my lesson. 😃 =P

In Pakistan, hardly any company sells high quality astronomy equipment so I'm stuck with my newtonian (which is an impressive instrument in its own). Over the years I've learnt the importance of having a small setup that is easy to transport to dark sky sites than having a big setup that stays stranded under my light-polluted urban skies. Maybe in the future, I would invest in a fast high quality refractor. But at this point in time, I'm wondering if a coma corrector can bring me peace and satisfaction of having crisp stars. Judging by so many comments on this post, I'm actually very hopeful that I won't be disappointed. So most certainly, I will invest in a CC very very soon. 😃

Thanks @Ronclarke and @Grimbles for sharing your coma corrector details. I'll be putting in my order shortly. Thanks a lot guys. You have all been a great help!

@JamesF thanks for that valuable insight. I'll look into skywatcher coma corrector. :-)

@Ronclarke and @Grimbles. Would you be kind enough to post a link to the coma corrector you're using? Perhaps if you could share pics that could show the difference your coma corrector makes to an image vs one without it.

And if I understand you correctly... You're saying that my images would be s lot better if I invested in a coma corrector and that I don't need to switch to a different scope, right?

Finally, I see that coma correctors have very different prices, some cheap, some expensive. What would you recommend for my scope? My scope has a 2" focuser. And would I need focus extension tubes to attach my dslr? Perhaps if you would kind enough to share a picture which shows how the CC fits into your optical train... :-)

Thank you so much for your responses. :-)

Hi,

I am a very proud owner of SkyWatcher PDS-200 F5 newtonian reflector and I've been using it for many years now. I think I understand the process of collimation well enough. However, even with my best efforts, I still can't get crisp stars. I've tried to ensure that my collimation is good. I've tried to ensure that my focus is good. But even then, my images suffer loads of coma.

One of the best images I've been able to snap is the following. If you zoom the image up to 100%, you'll be able to see how bad coma is at the edges of the frame. I am aware that newtonian scopes suffer from coma, but is it really as bad as in this image?

For a long time, I've been mulling over whether I should get a coma corrector (how is it different from a field flattener, btw?) or a different scope that doesn't suffer from coma. But I don't have answers to the following questions that pop up in my head:

1. Should I get a coma corrector? If so, how should I go about choosing one for my scope? Can you recommend a suitable coma corrector for my scope? Should I also get extension tubes for the scope's focuser?
2. Or should I get a different scope altogether? If a good coma corrector is gonna cost as much as a scope, I'll probably be better off getting a more portable scope. If so, which type of scope should I be looking at?

I know any discussion about possibilities for a scope is very open-ended, but I really just wanna get your perspectives on this problem of mine. Is my current scope good and am I using it wrong? Or is it bad but can be improved to perfection with a coma corrector? Or is it a lost cause and I should rather invest in a better (and more portable) scope?

Also, I would really appreciate if any of you guys can guide me how could I improve this image I've shot. This is one of my best attempts but it is nowhere near the awesome images I've seen elsewhere on this forum. I took this image from a really really really dark sky site. I shot it with a Nikon D5100 attached to my SkyWatcher PDS200 F5 mounted on an NEQ6 Pro mount which was polar aligned and tracked but without any PHD autoguiding (cuz I'm not very learned on the subject with regards to hardware required). The image is a stack of 10 images, each 30 seconds long (cuz my DSLR doesn't support computer controlled exposures longer than 30s). Any tips and guidance is most welcome. I would love to be shown how can I improve my skills.

Thanks,

Asim Sohail

Thank you everyone for responding to my query and sharing your thoughts on this issue. You guys have given me a lot more to think about, and well as raised more questions in my mind. I have updated the topic question in the first post to list these questions, as I didn't want to start a new thread for follow-up questions. If you have time to spare, please go through the edit I made to the question and share your thoughts.

Thank you for your invaluable advice.

Asim

4 hours ago, RolandKol said:

No problem,

Just keep in mind, - while imaging in Mono + Narrow Band filters, you will need guiding 100%, as due to the nature of the narrow band imaging, your exposures will be minimum 3min ( with CMOS astrocam) or even longer around 10mins (with CCD).
There are LRGB filters also, - which do not remove Light pollution at all, but it is the main set for Galaxies and brighter nebulas like Orion and etc and with CMOS you can get away with 30sec exposures.

As per Mono without the filter-wheel... I do not see myself enjoying it at all... As filters will have to be moved around quite often and at the end, - Flats will not match each session (dust and etc), which will make your  post processing quite difficult and time consuming.

or, - you will have to restrict yourself to "one night per one target" only... no fun... 

While choosing astrocam for imaging, as previously mentioned, -  look at the cooled versions only. Cooling will reduce a lot of noise, plus, you will be able to control temperature of the Dark subs, - in other words, you will be able to create the library of darks with the different exposures/settings in advance and do not waste imaging time during the night.
If £££ amounts becoming too heavy for your wallet (and probably will, as Mono + Filters + Wheel + Guider Set Up will most likely be around £2k+), - I would suggest to go guiding way initially, as it is quite challenging task at the start and needs experience to perform properly, plus if you choose fast colour guider camera, you can do planetary imaging or even hunt some galaxies like M51 or smaller ones while saving funds for mono setup

Thank you for responding Roland. I have gained new insight and knowledge from your reply. Thank you.

On 20/06/2019 at 14:17, ollypenrice said:

At some point it really is worth getting to the fundamentals with a clear head and that's what your post is about.  So...

- 'But from what I've read, web cameras usually have a resolution of just 640x480. Isn't this too low in order to get a good quality astrophoto?'   OK, the numbers 640x480 do not specify a resolution, they specify only  a pixel count, but how big are these pixels? In what follows I'm going to assume that we are talking about one scope of a given focal length. (Changing focal length also changes resolution.)

- Resolution is properly defined by the term 'arcseconds per pixel.' In other words, How many arcseconds of sky land on each pixel? The smaller the pixels the less sky lands on each one and the higher the resolution of detail. So pixel size determines resolution while pixel count determines the size of the chip and, therefore, the field of view the chip can image.

 - However, the turbulence of the sky in deep sky imaging blurs out detail at some point which may vary between a bit less than 1 arcsec and a bit more than 2. This means that there is no point in having pixels which are too small because the 'seeing' won't let them work to capacity, though with mono you can bin them 2x2 (read 4 pixels as one.) And the errors in the mount's tracking blur out detail as well. Your EQ6 is a good mount and can, with an autoguider, keep your tracking errors down to as little as half an arcsecond. Without an autoguider it will probably run at an error in the order of 20 to 30 arcseconds, which is an enormous difference. It is clearly worth autoguiding! No single addition can bring an equivalent improvement to your results. (Beware of using round stars as a test of tracking accuracy. If you have large tracking errors that are about equal in RA and Dec you will get round stars - big blurred ones.)

- Telescopes vary considerably in the size of the 'corrected circle' they produce. That means stars will only be sharp over a certain size of chip. If the chip is too big the scope won't 'cover it' as we say.

With all this in mind you need to choose a camera which gives a resolution in your scope which the tracking accuracy and the seeing will allow. FLO have a scope-camera calculator and there is another one here: http://www.12dstring.me.uk/fovcalc.php  Unless you autoguide there really is little point in going for a high resolution system at all. And don't buy a camera with a chip which is bigger than your corrected circle. Chip real estate is very, very expensive!

There is an important new possibilty for you as well: the astro- dedicated CMOS camera brings you cooling (as in CCD) and the advantages of mono (another story) at a far lower price than CCD.

Olly

Hi Olly. Thank you for that in-depth explanation. I clearly have to learn and understand a lot more than I currently do. As per your advice and Carole's and Roland's, I think I will settle for now on a Mono camera with fixed filters, then upgrade to having a guidescope and guide camera, and finally get a filter wheel. Does this sound like a logical order? Also, would you mind if I pm you some follow-up questions?

Thanks a lot. 😃

On 20/06/2019 at 13:22, RolandKol said:

I will second Carole and will offer the same,

If you have got funds, jump into mono without wasting time on DSLR or color astro-camera. Mono cost a lot as you will need to buy filter wheel and filters in addition, - but it worth it by all means.

I was in your shoes one year and a bit ago, and I simply could not justify the Price of Mono, but the more topics I read on this matter, the more advise Topics I created myself, - the advise was just one, - "Go Mono".

There are 2 main options for Mono: CCD (like Altair) and CMOS (as ZWO Asi for example). CMOS is a bit cheaper option with it's challenges, advantages and disadvantages over CCD.

As per "fix Nikon" + Guider... it depends on the area you are in... I cannot do longer subs than 30sec from my back-garden in London as they get overexposed even with ISO100, and I can easily do 30sec without a guider.

P.S.

For guider cam, if you will decide to get one, go for something like ASI 224MC, it is a nice guider CAM and plus, - quite a good camera for Planetary imaging, plus it has quite a small pixel size which has some impact on a better guiding.

Hi Roland. i appreciate that you do seem to understand my confusion and thought process. Thank you for your valuable suggestion. I do believe that I should save for a mono cam and filter wheel. If I have some more funds, I would even try to save for a guidescope and a guide camera as well. From what I've read on Carole's blog, a mono camera and filter should work quite well even in light polluted areas due to the fact that they let in such a narrowband. Thank you once again. 😃

On 20/06/2019 at 13:20, alacant said:

Hi

How about one of these for the planets? Then use it in a guide scope for your deepsky frames. Either get your d90 fixed or a cheap eBay canon?

Cheers and HTH

Hi. Thanks for your take. Your suggestion will definitely help me make an informed decision. 😃

15 hours ago, carastro said:

This is my take on your question.  

I started with a DSLR, and wanted to get better detail/reduce noise so decided back in 2012 to buy a CCD camera.  Many people advised me to get a Mono camera and filters because mono gives more detail due to the lack of a bayer matrix.  This is more expensive because of the need to purchase a filterwheel and filters.  But I took their advice and bought a mono camera and filters.

My DSLR was still usable and on my first weekend at Kelling armed with both my DSLR and my new Mono CCD camera I took images of the same target with each on alternate nights, more as a test than anything.  I was completely blown away at the results of the Mono CCD camera compared to what I could get with the DSLR.  

It took me a little while to learn how to combine the different colour filters, but since then I have never looked back, and very rarely now use the DSLR for imaging,  

About a year after I started mono imaging, I got an idea to buy a OSC (colour) CCD camera and take simultanous images with the Mono camera so I could get data more quickly.  That OSC camera caused me a lot of hassle, and the results were not as good as those I could get from my mono camera,  so I dispensed with the colour camera and just stuck to mono imaging.

As an added bonus you can take narrowband images with a mono camera (OK, I know some say you can take narrowband with a colour camera too, but is it the same quality and does it take much much longer? )

There are many targets that really show up best in narrowband.

Personally I would not waste time and money mending your DSLR. 

HTH

Carole  

 

Hi Carole. Thanks a ton for your valuable advice. I had a look at your site as well and have bookmarked it to go thru it all. I found an in-depth blogpost you shared there too titled "Why change from DSLR imaging to CCD camera". I will be taking a closer look at your equipment to refine my selection of cameras. Thank you for sharing your views. And thank you for taking time out to explain all this in-depth to a novice like myself. 😃

Hi,

I have a SkyWatcher P-DS 200 telescope and an NEQ6 Pro SynScan mount to go with it. I've done plenty of astrophotography over the past year or so using my Nikon D90. My D90 recently suffered hardware failure and is no longer usable for imaging. So I'm trying to build up my knowledge of what to look for to replace and improve my setup as far as astrophotography is concerned. I've tried using my google skills to gather knowledge but it hasn't proved very fruitful so far. Thus I am turning to you guys to share your wisdom. I love doing photography of deep sky objects and planets equally.

1. I understand I need to invest in a CCD imaging camera, but there are so many options in so many different price ranges. I've read about using web cameras for imaging. But from what I've read, web cameras usually have a resolution of just 640x480. Isn't this too low in order to get a good quality astrophoto? Also, I believe web cameras are not capable of taking long exposures (say, over a few seconds). Instead they take video which is processed in registax or iris or a similar software to work with individual images. On the other hand, I've seen really expensive CCD cameras like those from Altair that are not even color. Should I invest in a web camera capable of taking poor resolution video or invest in a decent camera from (say Altair), or I should abandon this route completely and have my D90 repaired? I would love to be able to image in color. How should I decide which of the 3 routes should I go? And what should I look for in choosing a camera? Sensor size? Megapixels? Brand? Color or black and white?

2. I don't have an auto guider, and don't know much about its limitations. Till now, I've constrained my exposure to less than 30 seconds. Should I save my money by not getting a CCD for primary imaging and repair my D90 instead, and instead invest in an auto guider scope and camera instead? If I don't invest in an autoguider, will a CCD camera (like Altair) not be an improvement over my existing D90 at all?

I am aware that most of us here have taken small steps in this hobby: incrementally updating our kits. I don't have that luxury partly because I live in a country where astronomy equipment is of nobody's interest. So I have to have a friend bring it back from a trip abroad, which isn't very frequently. Also, there is no second-hand market here that I can sell my old gear to before upgrading incrementally. So I would prefer to future-proof my investment by getting gear that I will not have to replace/upgrade anytime soon. Even my SkyWatch PDS 200 and NEQ6 were brought many many years ago and are still serving me well.

I know these are very subjective questions and there might not be a definitive answer. But I would love to hear your thoughts as to how you would solve this conundrum if you were in my place.

Thanks everyone!

Asim

-------------------------------------

Edit: After going through all the responses posted to this topic, I have realized that guiding is a must if you're using narrow-band filters since they let in so little light that very long exposures are required. On the other hand, I have some follow-up questions:

1. Why is it that mono cameras are more expensive than color cameras? Technically, color camera is giving you three channels worth of data whereas mono is giving you three times as long an exposure. But I fail to understand why is there such a cost difference.
2. It's possible to use a color camera without any filters. But is it possible to use a mono camera without filters too? Would it see all visible wavelengths and render them as a greyscale image? If so, technically, I can get a mono or color camera first, and then get a filter wheel + filter set. Am I correct in assuming this?
3. Carole, you mentioned in her blog that filter wheel caused a headache for you due to light leakage. Which is why I thought a better way might be to simply use individual filters when needed. But the lovely people in this thread seem to believe that this is not a big issue. Should I try to save more and get a camera with built-in filter wheel, or should a separate filter wheel be just fine too?
4. I understand that for planetary astrophtography, I would benefit from the camera having a smaller pixel size since planets appear so small on the sensor in the first place. On the other hand, DSO photography might not benefit as much from small pixel size. Is my understanding correct?
5. Where does pixel count become relevant? I've seen cameras having 2 million pixels cost more than ones having 20 million pixels. Why would this be? I believe that small pixel count (sensor size) cameras are more suitable as guide cameras while larger pixel count cameras are suitable as main cameras. Is my understanding correct?

Finally, consider the following cooled cameras:

ZWO ASI183MC | Color | 15.9mm sensor | 20 mega pixels | 2.40µm | EUR 960
Altair 183C | Color | 20 mega pixels | 2.40µm | EUR 980
Altair 183M | Mono | 16mm sensor | 20 mega pixels | 2.40µm | EUR 1129
ZWO ASI183MM | Mono | 15.9mm sensor | 20 mega pixels | 2.40µm | EUR 1149
ZWO ASI294MCPro | Color | 23.2mm sensor | 11 mega pixels | 4.63µm | EUR 1197
ATIK Horizon Color | Color | 21.9mm sensor | 16 mega pixels | 3.80µm | EUR 1399
ZWO ASI1600MM | Mono | 21.9mm sensor | 16 mega pixels | 3.80µm | EUR 1499
ZWO ASI1600MMPro | Mono | 21.9mm sensor | 16 mega pixels| 3.80µm | EUR 1533
ZWO ASI071MCPro | Color | 28.4mm sensor | 16 mega pixels | 4.78µm | EUR 1779
ATIK Horizon Mono | Mono | 21.9mm | 16 mega pixels | 3.80µm | EUR 1789

Should I aim for [Altair 183M Mono] camera from this list? It's the cheapest out of this lot, is mono, has very small pixels, and has a high pixel count.

Thanks,

Asim

awesome read!!!!

i was gonna post in the existing thread with the same name but it was closed..

im from pakistan with no dealers of telescopes nearby.. a friend is due to come back from norway in a months time.. i was going to opt for FLO but the shipping costs were high.. i stumbled upon telescop service thru skywatcher's dealer listing.. and what an experience has it been..

although i havent ordered yet (im busy with some work and will order in a week or two when im free).. the service is absolutely wonderful..

their website states that if youve seen an item cheaper elsewhere contact us and we'll give you a better offer.. i just gave it a shot in the dark when the NEQ6 on their site cost almost 100 EUR more than at FLO.. they replied promptly and gave me a quote that was lower than FLOs as well.. i was impressed.. thats when i decided to go for their service.. over the course of a month.. ive exchanged almost 20 emails from mr. helmut eichler.. and ive bugged him repeatedly.. asking him to provide me with a quotation on one list of items.. and he responds soon.. then my decision shifts and i email him an alternate list.. he still responds.. and then my decision shifts again.. hes been so patient that it amazes me.. if i were in his place id be close to telling the customer to make up his mind first..

hes guided me along very well.. postage charges.. delivery time.. discounted offers.. package weight and dimensions (since im having it brought by air).. ordering options..

the stores policies are really good.. sure i cant compare it with the rest since this is my first time.. but they get a thumbs up from me without a doubt..

will share more when ive actually ordered.. but to date.. ive been impressed with them.. i hope they keep their good image in my eyes.. if they do.. theyd find me a regular customer of theirs.. ..

awesim

hi.. asim here.. and what an awesome forum has this turned out.. i came here to help me decide the scope i should be getting.. its been almost two months and ive been totally immersed in the site.. ive learnt so much in such a short period of time from the members here.. it wouldnt have been possible if i hadnt hit this forum.. the members are so willing to help.. they ignore the fact how stupid your questions sound to them.. and patiently answer over and over again TILL YOU GET IT!!!.. .. this has literally turned out to a gold mine of knowledge for me.. if i could i wouldve used a spider to download ALL the posts so far for future reference.. cuz whatever problem you have.. someone has a work around for that.. but i wouldnt wanna miss the new posts that spring up every second.. you wouldnt learn even one hundredth as much in a paid specialist course like imaging etc as you learn here.. a MUST bookmark in every star gazers browser..

one brilliant thing.. 50 posts and one month membership to be able to access the BUY AND SELL forum.. if it wasnt i wouldve jumped in.. brought a scope without thinking much.. and regretted..

one recommendation.. keep it up.. its perfect..

love this forum.. love its people.. =)

@adz.. great review pal.. im almost done planning to order SkyWatcher Explorer 200PDS.. the mount may be different but the OTA is virtually the same.. the images you posted helped my clearly visualize what id be getting in my boxes.. a review very well done indeed.. good job.. ..

hi.. ive been seeing references to FLO thruout the forum but i cant get any details on it.. i assume its a dealer in uk.. but can someone provide me with its website address or something? i dont live in uk so bear with me..

asim