rnobleeddy

I owned a 450D that someone else modded. Aside from dust (which wasn't an issue for me) I got on fine by adding 2" UV/IR cut filter to the optical train with a full spectrum mod.

A basic filter may only set you back £30, so that's an option to consider if the parts are expensive or hard to fit. 

On 02/04/2021 at 16:35, CraigT82 said:

In your shoes I'd probably use a 2.5x or 3x amplifier. For hi res work you need to make sure scope is as collimated as you can get it and that it is cooled and thermally stable. Consider fans and/or wrapping of the tube. Also need to consider what you're shooting over and try to avoid houses or car parks. Shooting over fields is better but may not be possible for you. 

Try to image when the moon is up high, I've got my best images up above 45 degrees although nice results can be had when lower. 

If seeing is so-so then use red or IR filters. Good seeing might call for a green filter and excellent seeing might support a blue filter for the finest resolution your scope can give. 

During capture you want to ignore the histogram as Vlaiv says. You dont want any blown out highlights so keep an eye on the rims of craters etc. The image will look dark in the preview when properly exposed, but with processing a lot of detail can be teased out of the shadows.

Focusing is critical so spend time on that. Don't bother with bhatinov masks or any focusing aids... get the preview image zoomed in and watch the fine details carefully as you rack the focuser in and out through the focus point. Make small adjustments and observe the image carefully after each adjustment. I would say that motorised focus is essential. 

You don't need huge capture sessions really, I find that 5000 frames captured and stacking maybe 500 best frames yields good results. 

Hooe that helps, good luck!

 

Thanks. How far away does the ground matter? I have a clear view over fields to to the East, and have a couple of hundred meters to the south, so hopefully I'll have opportunities. 

Any recommendations for a barlow? My current camera would need a 2" barlow, so it's probably worth considering a smaller planetary cam  + a 1.25" barlow as well. 

On 02/04/2021 at 12:50, vlaiv said:

Diffraction limited field of Newtonian is given by following expression:

https://www.telescope-optics.net/newtonian_off_axis_aberrations.htm

With F/5 scope that gives 1.389 mm from optical axis or 2.77mm diagonal. You need to select your ROI to that size (or that size amplified by barlow lens if you use one).

 

Would it be worth using a coma corrector here? 

Quote

- You can use lower sampling rate than critical sampling rate - but I would advise against going over critical sampling rate as it really does not do anything for image quality and only lowers SNR. You can calculate F/ratio that you need for given pixel size by using following formula:

F_ratio = 2 * aperture * pixel_size / wavelength

F_ratio = 2 * pixel_size / wavelength

(aperture is already in focal ratio, formula with aperture is for focal length instead)

Use same units of length for all quantities (say micrometers for all).

(reference: https://en.wikipedia.org/wiki/Spatial_cutoff_frequency, https://en.wikipedia.org/wiki/Nyquist–Shannon_sampling_theorem)

 

Thanks. Based on this, with this camera, a 2x barlow would probably suffice for Ha wavelength. I'll have a think though - a decent 2" barlow isn't cheap so I may consider something like a asi178mm-mono, as I also could also use it as a 2nd guide camera to prevent swapping kit as much.

21 hours ago, wookie1965 said:

You can make one out of a exercise mat. 

+1 for this. Mine is still going strong after being well used this winter.

4 minutes ago, vlaiv said:

Here are some guidelines to help you out.

- Newtonians have diffraction limited field that is way smaller than the sensor you are planing on using, so if you want to use that camera (or that is your only choice) - you'll probably want to use ROI - region of interest.

- ROI helps with achievable FPS (smaller ROI enables for higher FPS because less data needs to be transferred over USB link, but there is a limit). You are right about the Moon allowing for much smaller FPS rates, but the Moon does change over the course of the night. It is not as obvious but it does change both size and orientation as well as position with respect to the Sun - which in turn changes level of shadows. I have not researched this matter extensively but I'll suggest that you keep your sessions limited to maybe half an hour?

- Smaller ROI means you won't be able to do full disk at once - that is what mosaics are for - so research how to shoot and stitch those

- You can use lower sampling rate than critical sampling rate - but I would advise against going over critical sampling rate as it really does not do anything for image quality and only lowers SNR. You can calculate F/ratio that you need for given pixel size by using following formula:

F_ratio = 2 * aperture * pixel_size / wavelength

Use same units of length for all quantities (say micrometers for all).

(reference: https://en.wikipedia.org/wiki/Spatial_cutoff_frequency, https://en.wikipedia.org/wiki/Nyquist–Shannon_sampling_theorem)

use Barlow lens to achieve close to critical sampling rate if you want the most resolution out of your images

- Use narrowband filter to tame atmosphere. People often use Ha filter or IR pass filter or Baader Solar Continuum 540nm filter when doing lunar with mono camera

- Don't use histogram to set your exposure, in fact don't look at histogram at all. Set your exposure length below 5-6ms to beat the seeing

- Use very high gain settings - as that lowers the read noise. Read noise is one of your worst enemies here

- Do proper calibration (means take darks, flats and flat darks)

Diffraction limited field of Newtonian is given by following expression:

https://www.telescope-optics.net/newtonian_off_axis_aberrations.htm

With F/5 scope that gives 1.389 mm from optical axis or 2.77mm diagonal. You need to select your ROI to that size (or that size amplified by barlow lens if you use one).

 

Thanks Vlad - very helpful as always. I will do the maths later and see how it looks!

3 minutes ago, CraigT82 said:

What kind of images do you want to achieve? Close in shots of individual features or full disk?

 

Yeah, should have mentioned that. 

I guess I'm looking for close in shots or high-res mosaics. I've had a few goes at capturing the full disc and processing with autostakkert/registax already with OK results.

I'd like to get in to lunar imaging this summer, as a way to have something to target whilst the nights are lighter. I was hoping someone could help with some advice on kit.

I already have a either a 200PDS (1000mm) or 250PDS (1200mm) Newtonian available and a QHY163M. FOV for the camera/250PDS is below. The camera should manage a little over 20fps at full res/8-bits.

I've been trying to get a little more scientific in the way I approach DSO, and so my questions are around what is most important as I move to lunar imaging.

- Is there anything fundamentally wrong with the plan to use this kit? I realize the pros don't use Newtonian's but I'm guessing this is primarily because there are more practical longer focal length scopes, and a higher f-ratio isn't an issue for lunar work? 

- This camera, with the 1200mm scope, leads to a resolution of 0.65" per pixel. I understand the principle of lucky imaging and have seen suggestions that lucky might mean as low as 0.1" , but not sure what's a sensible expectation? Assuming I'm under-sampling for lunar imagine, would a barlow or powermate be a sensible option?

- As the moon doesn't suffer from much rotation, is the lack of fps an issue, or can I just record for longer? I guess this also comes down to a question of whether it's better to collect more frames at a lower FOV? I don't know what's considered top of the range for lunar imaging, but I'd guess over 100fps is easily achievable, but probably with a smaller chip.

Obviously I'll be trying it out anyway, and I'm keen not to spend too much extra, primarily because my view is blocked to the south (below approx 30 degrees) and so Jupiter/Saturn are generally not visible and so whilst I might get mars sometimes, I can't really do a lot of planetary imaging. That said, if a cheapish longer focal length scope or a new camera would help a lot, I wouldn't rule them out.

3 minutes ago, Newforestgimp said:

I have been considering Raspberry Pi with astroberry or stellarmate, any experience of the WiFi range ?

at the moment I RDP into my laptop (that is cabled to the mount) to keep an eye on proceedings which is working well, but think a mini PC would just tick the boxes when using away from home.

My Pi has worked fine attached to a leg on the mount, with wifi repeater near a garden window.

It suffered from occasional drop outs/slow down when attached to the OTA. Presumably the metal tube kills the signal, and in the garden, there's no walls for the signal to bounce off like there is in the house.

36 minutes ago, Mr Thingy said:

I think I would feel most comfortable with some weather equipment. 

Interested to know what is available, short of installing a radar station (wife might not be impressed with a radar on the roof).

I guess you can fit a rain sensor but if it triggers then it's already too late.

 

I guess that's depend. I'd imagine most kit would survive a little rain, so perhaps a rain sensor plus the app would work? 

4 hours ago, ollypenrice said:

Power cuts? Cable connections? PC shut-downs? Eventually, if something can go wrong it will go wrong. Some people, for instance, would robotize a roof which required the scope to 'park' first and some would not. I certainly would not. One day it will happen...

Olly

I don't really mind losing data - it's not worse than not having left it running in he first place.

A mount collision may cost me a £70 replacement motor but power cuts are very rare.

Rain is the big killer, but there are definitely nights where I consider the forecasts to be accurate enough.

On 26/03/2021 at 19:59, Daniel Karl said:

Hey all,

I'm new to this forum and currently on the brink of breaking into the hobby again after almost 15 years of break.

I used to take photographs on 35mm film with a 15" f/4.6 Lomo Newton on a 200pound (excluding scope, counterweights or tripod) beast of GEM (ALT-7 ) - with all the fun of manual off axis guiding in -15 degrees under Bartel 3/4 skies.
Now I live in London, don't have the strength to lift 200 pounds any more and never dreamed of trying to do astrophotography here.
But then I accidentally stumbled over some of the images taken in not much better conditions with relatively small Optics and suddenly I am thinking about buying a telescope setup again.

After a couple of weeks of reading it seems that a 100/120 Apo with something like an ZWO1600MM on an EQ6-R Pro could get half decent results even under London skies and is still small enough to fit in the car for a trip to Wales (if we're ever allowed out again).

Then I wondered if I even need apochromatic optics if I have to use narrow band filters anyway?
Registration might be a problem if the different filtered components end up with slightly different focal lengths, but that might be solvable with relatively simple scaling?

I have found a few posts discussing this, but I couldn't quickly find any comparative examples or photos taken with achromats and narrowband filters, so I figured perhaps you guys have any thoughts about it?

Cheers,

Daniel

If the kit you choose isn't too heavy, consider a HEQ5 mount over the EQ6. I've got an EQ6 and whilst you can certainly pack it up in the car, it's only worth the extra weight if you need the extra capacity. 

YMMV and there's loads of options for tuning, but I don't get the impression that guiding performance is significantly worse on an HEQ5. And it's a little cheaper.

6 minutes ago, gorann said:

I agree with Vlaiv on the camera. The ASI1600 is now a bit outdated and the ASI294 would be my obvious choise for a camera with that sensor size. There are now lots of ASI1600 on sale on the used market - I think that people are upgrading to the more sensitive next generation of CMOS, like the 294, or the amazing 2600 with no amp glow.

If you're buying new this is very sensible advice.

If you're considering second hand, I've seen 2nd hand ASI1600s (or equivalent) for less than 1/2 the price of a new ASI294. Of course, a second hand 294 would also be a good shout, but I've seen very few for sale, whereas there's been a lot of 1600's on offer recently.

All the time. I doubt it's be possible for me to do this hobby if the equipment had to be manned. Not many overnights yet as it's rare that it's been guaranteed to be dry but in the winter there were lots of 6 hour+ sessions where I set if off and checked in rarely.

I've found meridian flips in EKOS to be  a little hit and miss, but it's often possible to choose a target that won't require a flip, and just automate the mount parking at the end. Others appear to get flips to work well, but in any case, it's only been an issue with alignment failing so the data being poor. Ditto with focusing - it's great most of the time, but all it's gonna cost is data.

My EQ6 is old so I'm not too precious about it - it crashed in to itself once and made a pretty nasty noise, but doesn't appear to have caused any lasting harm.

Use telescopius (or equivalent) to help find decent targets that are as far away from the moon as possible. That said, I've had little success with galaxies under full moon - whereas ha targets 40 degrees+ away from the moon look better. 

Definitely 4 hours. I can't remember ever regretting more data on a single target whereas I routinely get rubbish data because I get too optimisitc!

Thanks - just to follow up in case someone finds this in future:

https://forums.atik-cameras.com/index.php?topic=329.0 has a decent looking dumbbell using GRBG (and the red is in the right place) but I concur with @JamesF the the manual says GBRG. 

Either way, the G's are in the right place - those two both look possible, but the other two look awful. I've up given up on the data I collected on M101 but I'd also grabbed a few subs on M13 if has an eye for color. This was the best 25x30s frames from a cloudy night processed as GRBG processed super quickly- so all things considered, the 15 year old camera is doing OK!

I'm leaning towards GRBG , but if I definitively work out the correct bayer matrix in daylight, I'll update. 

22 hours ago, Gaurav Mk said:

Thankyou. I have the non go to basic EQ5 mount and I have added RA DEC motors and have a hand controller with st4 port. 

As I see the cable showed in ur case, eqdir, has one end with usb connection and another with st4 connection. So I think it should still work and eliminates need to have st4 port on ur laptop as well. Right? Please correct if my understanding is wrong. 

Thanks again for all the info

Unfortunately it's not quite that simple. The end on the cable you saw isn't ST4, but a similar looking cable that plugs in to the control box on a GOTO EQ5.

Eqmod replaces the GOTO handset with your PC and also enables pulse-guiding.

With the standard RA and DEC motors you're going to be limited to ST4 guiding.

The good news is I had this setup and I didn't find guiding was any worse (I later upgraded to GOTO) - the only problem is finding the target manually can often be a challenge! 

I've found that I can leave my mount setup in the garden under a decent quality cover. It's been out for about 4 months now and aside from some small patches of rust (counterweights, counterweight screws) it doesn't appear to be suffering. Makes a big difference, as it holds PA really well, so I can be imaging in about 10 minutes.

Realize this is a super old camera but wondering if anyone knows the bayer pattern? 

I mainly got it as a guide cam but as it was about the correct FOV for some galaxies I decided to try it out for imaging,

I'm using it with Indi/Ekos which reports it as RGGB but this looks awful. One of the other early 314 models was (apparently) GRGB which is better, but I'm still convinced about. 

Obviously there's not a lot to try, but it's one of those situations (not enough in poor conditions) where I probably won't be able to tell from the image itself

1 hour ago, vlaiv said:

Not sure what you mean by this - but even if stars seem small or large in the image (bright or faint) - they will have fairly similar FWHM value. That is why FWHM is used as a measure of things.

FWHM will depend on where in the sky your scope is pointing. Out of 3 things that impact resulting FWHM the most - two depend on where the scope is pointing.

Seeing is usually the best in direction of zenith and degrades as you move down towards horizon. This is because light has to travel thru thicker piece of atmosphere so it has more chance to get distorted along the way.

Guiding performance also depends on where the scope is pointing. RA error is the worse at equator - but it gets smaller as you increase declination and move towards NCP. If you think about it - Polaris takes 24h to make very small circle on the sky - you can fit that circle on your sensor with ease. Path that Polaris takes is something like maybe few thousand pixels - and it takes 24h for it to make it. Close to north celestial pole - large movement in RA results in very small movement in pixels on sensor - this also means that any error in RA will be very small when translated into pixels. Star won't be smeared as much due to RA error close to NCP. At 60° declination RA error is effectively halved because of this effect and continues to drop (times cos declination).

Sorry - I wrote that without thinking about it. Unfortunately whilst I did study physics, I've since forgotten everything I ever knew . But I can learn again!  

DSS reports average FWHM ranging from low 3's to mid 4's across a few different stacks. As best I can tell, these are average values in pixels, so that's roughly 3.6" to 5.5". Just trying to work out if there's any decent way using free software to get a better idea of the spread of the FWHM.

Edit - I'm using the relatively cheap Baader MPCC, which I also imagine isn't helping.

Do you mean 9x50mm? If so, it's very common - for example with https://www.firstlightoptics.com/adapters/astro-essentials-sky-watcher-9x50-finder-to-c-adapter.html (and there's a T-thread version available). I use a similar ZWO camera like this.

If it's 8x50mm then I'm afraid I'm unsure if it's the same. But for example, the 200PDS ships with the 9x50 e..g. https://www.firstlightoptics.com/reflectors/skywatcher-explorer-200pds-heq5-pro.html 

6 hours ago, pete_l said:

Two points/

First, you can always alter your arc-sec per pixel value by adding a focal reducer. That will give you the benefit of the larger aperture.

Thanks. Are there general purpose reducers for Newtonians? I've seen some coma correctors that change the focal length a little.

Quote

 Second, you say the setup is too unwieldy for one person to manage. That would seem to shut down any further discussions about using it.

I guess I should probably have said it's not ideal but not impossible. I can't seem to work out a way to screw the dovetail on to the mount on my own, as the mirror is so heavy and the scope too large to reach around. But I can almost always get help setting up, and I did manage to take it off the mount on my own. Longer term I'd probably just get a cover that I can use until the morning, but I've got the 130PDS routine down to less than 5 minutes at either end of the night, so it maybe just feels like a lot more hassle!

7 hours ago, vlaiv said:

As far as choosing imaging resolution goes, here is the quick break down:

1. Seeing FWHM somewhat relates to imaging resolution but it is not straight 1-1 correspondence

2. Aperture size and your guiding / tracking play a part too

3. Seeing + aperture + guiding will give you some final FWHM of stars in your image. This is usually larger than what would seeing alone produce. Having stars of 2" FWHM or less in your image is rather difficult to achieve although seeing of 2" FWHM is common

4. There is simple relationship between sampling rate and FWHM - which is star FWHM / 1.6 = sampling rate.

In my view 1.2"/px is oversampling on 5" aperture in regular seeing and tracking conditions. Say you guide at 0.8" RMS and your seeing is 2" FWHM - what would be good sampling rate?

You can expect star FWHM to be 2.88" and corresponding sampling rate around 1.8"/px

Examine some of your subs that you've taken with 130pds to get the idea of what FWHM you can expect. By the way - above is for perfect optics. For example, newtonian with simple 2 element coma corrector will bloat stars somewhat due to introduced spherical aberration and you can easily have stars with FWHM 3" or 3.5" in your subs because of that.

250PDS will have large aperture and this means a bit tighter stars. In same conditions as above - 2" FWHM seeing and 0.8" RMS guiding, you'll get 2.78" star FWHM instead of 2.88" star FWHM - so there is a bit of improvement. In fact - better the seeing and your guiding - more improvement you'll see over smaller aperture.

However, even scope that large requires good seeing and good guiding to hit 1.2"/px resolution. In 1.5" FWHM seeing and 0.5" RMS guiding, ideal 10 scope will produce stars with FWHM 1.96" and corresponding sampling rate will be 1.22"/px

In any case - not all is lost - you can bin your subs in software after calibration to get to good sampling rate.

Bottom line - increased focal length may give you larger objects - but not more resolution. You'll get same effect if you simply enlarge your images in the end - larger object without additional detail. In order to really get detail - you need sharp largish optics (say 8"-10"), exceptional mount that tracks/guides smoothly (rms in range of 0.2-0.3) and night of very good seeing (1.2-1.5" FWHM range).

 

Thanks - really helpful explanation. 

Guiding with the 130PDS currently ranges between 0.7" and 1" depending on conditions/balance/wind/target position. Usually about 0.8".  I guess I'll need another night to work out how much that degrades with the 250PDS.

I'm guessing it is fair to assume most images will have some stars in them that are small, so it won't be dependent on where in the sky I was targeting?

If all else was equal, is it fair to assume the 250PDS has 4x as much light hitting each pixel as the surface area of the aperture/mirror is 4x, or is that maths more complex?

8 hours ago, michael8554 said:

Your own figures say it all.

130PDS ....... 1.2" per pixel

250PDS.......  0.65" per pixel

So you have nearly doubled your "magnification".

1.2arcsecs/pixel is an okay image scale for even UK conditions.

180mm guidescope with a 3.75um pixel guidecam, properly mounted, will work.

But the 1200mm FL is crying out for an Off Axis Guider with a Binned mono guidecam.

I don't know if that lot is too much for an EQ6 or not.

Michael

 

 

 

 

 

It's within the spec of an EQ6 but mine is a little stiff so I think it's hard to balance. I'm planning to belt mod it once the nights get lighter, so will have a go at sorting it out then.

The calc I found based on the pixel scale of the guide cam + imaging cam etc came out at about 240mm, so I guessed 180mm would probably suffice in a pinch.

From what I've read 1200mm is about the limit after which an off-axis guider is essential - do you expect that the performance is likely to be limited by the guiding at that focal length?

I've been imaging using a 130PDS on an old but passable EQ6 for the last 9 months or so. Most recently with a QHY163M + FW, but I've tried a few cameras over the months. Mainly DSOs but might focus on lunar work in twilight over the lighter months.

Someone nearby was selling a 250PDS so I thought I'd get it to give it a go, mainly as I was always a bit annoyed that some of my favorite images (e.g. the dumbell nebula, globular clusters) were so small. I guess I did this without really thinking it through.

I got the 250PDS out last weekend, and had the usual first usage issues - focusing with no idea of where to start was hard, and my attempt to barlow a cheap refractor to make a guidescope ended up in failure, and so I ended up guiding with a 180mm guidescope in the finder shoe. My EQ6 struggled a bit under the increased load, and I don't have a flat panel that's anywhere near large enough for the 250PDS.  But most of all, it's impossible for to safely get it out of the house/in to the garden without help, and that help usually goes to bed before midnight. So perhaps this isn't long for my collection.

I've resolved to have another go before I sell it, but I also started to think about what I was hoping to achieve. The 130PDS + QHY163M end up at a resolution of 1.2" per pixel, which as I understand, is going to roughly the same as a good nights seeing? The 250PDS ends up at 0.65" per pixel, which is (according a google search) the best seeing you'd ever get on Earth and I don't think they mean my garden!

So I may be doing this somewhat simplistically, but I'd guess this would mean the 250PDS is collecting ~4x as much light as the 130PDS I'd expect to collect more signal more quickly. Based on seeing, I'm not going to get a better resolution? So does it make sense to use the 250PDS? 

Hoping someone can sense check my ramblings above - which if true, mean that the 250PDS isn't going to "zoom" in on objects at all, so I've just got to weigh up if the size/weight is worth the extra light?

Given that the 250PDS is impractically large for someone who doesn't have an obsy, are there other scopes that people would recommend for this kind of work? Or should I just stick with the trusty 130PDS?

12 minutes ago, MarsG76 said:

Do you know this for a fact??? I seen similar statements online in various forums but no head-head comparisons.

My 40D is cooled so thermal noise is of no issue...

Eitherway, my 2600MM should be here within days so I'll compare the two and see the difference between the two when used in real world practice... graphs and company generated numbers hardly ever reflect real life use.

I don't know how accurate it is, but see https://www.dpreview.com/forums/thread/2750802 - if that's believed, the older DSLR sensors are quite a bit worse.

Anecdotally, I also owned a colour Atik 383 which is famed for having one of the worse QE of any astro camera, somewhere in the 40s. I didn't find that a massive improvement over my DSLR.