Upgrading from 130p for imaging

[LouisJB]

and back-focus, I'm still unclear. 130p is no good for my dslr out of the box but a 150p would be? yet doesn't have as much as the 150pds? If so, is there still a chance I won't have enough with the 150p unless I get the PDS version? and then it might slip

[RikM]

Coma correctors are 2" fit I am afraid. The standard 130P is only 1.25", where the 150P and larger single-speeds are (now) 2" with a 1.25" eyepiece adaptor.

As Uranium235 says, you can generally tighten up the tension screws etc. and furtle a focuser into usability.

[RikM]

I don't know how much backfocus is required with a Pentax camera, but with my standard 150P I have used Canon 300D, 1000D, 1100D and a Starlight Xpress SXV-H9 with a Brightstar manual filterwheel. These all reach focus with about 10mm in-focus travel still left.

[LouisJB]

ok, so I shouldn't worry about PDS over P in terms of focuser. But I should avoid getting more optics (coma corrector etc) that is the wrong size or requires yet more adapters!

So, in terms of back-focus, I guess it's difficult to say but it sounds like with a PDS i'd definitely be fine, with a 150P it's likely to be ok also, but there is less margin (say I wanted to dabble in OAG that might fail by making the optical train too long).

I certainly don't mind tinkering with a focuser to get it to work well, I'm more worried about starting out with the right things. By the time you've purchased a load of adapters, threads and bits and bobs it can be the price of a tube, so starting with the right focuser compatible with larger models sounds a better way to go.

In terms of coma corrector, I would just need a 2" threaded one that is compatible with the speed of the tube, so an F/5 one, no other parameters matter?

One other thing, focal reducers, would they help get a wider field, I see 0.5x reducers, do they work? 

[RikM]

Reducers do work very well but are easier to use with refractors and SCTs. As the optical speed gets faster things like collimation, orthagonality and focus get more critical. This is fine for an F/7.5 refractor reduced to f/6.4 or an SCT reduced to f/6.3. But a cheap Newt reduced to f/2.8 too much like hard work for me thanks.

[RikM]

This is the right one for the 130PDS http://www.firstlightoptics.com/coma-correctors/skywatcher-coma-corrector.html I don't know if it will work with the single speeds. The 0.9x reduction moves the focal point in towards the tube (opposite effect to a Barlow) but I don't know by how much.

I use the older type II version of this http://www.firstlightoptics.com/coma-correctors/baader-mpcc.html It sits down inside the 2" focuser drawtube. You can just see the top of it with green writing on. That shows how much focus travel I have left with the CCD gear. With a Canon DSLR it is more or less the same. Perhaps a couple of mm further in.

If you haven't guessed already, astrophotography can be a money pit if you let it. 

[Uranium235]

Definitely!

Avoid using anything other than a coma corrector with a newt. Or the quality of stars will put you in a...... coma. 

Unless its a corrector/reducer specifically designed for the job, like the ASA 0.73x reducer - which will set you back nearly 750 quid, with no promise that it will give you perfect results. Play it safe, stick to prime focus as f5 is plenty fast.

[LouisJB]

Hello, I'm resurrecting this thread as now I've had time to think and play around I've come towards the conclusion to:

1. Get a 150PDS OTA

2. Get a matching Coma corrector (0.9 skywatcher probably)

3. Sell my complete 130P on original EQ2 mount as the tube will be replaced by 150 and that is too big for EQ2 even as a portable/visual only setup.

However, that leads me to wonder, cost of tube + coma corrector is around £330 ish (new).

Is this a good choice? I know the ED80 comes up a lot for beginner imaging, problem is other than the odd shot of M31 I think I'd mostly like to image things like M27, M81, M82 etc, i.e. the easier of the DSOs but not the really really big ones like M31

Ultimately I would like the 8" RC but at 1500mm that's a different type of imaging and would probably set me back in terms of guiding.

Should I consider anything else in the mid-widefield area around F5, the quattros or orion F4 tubes perhaps? Or should I just go for the RC and solve the new issues, they must be solvable?

I think my guiding is working well, it stays guiding seemingly indefinitely (or until clouds come over!). However, I would like to keep the HEQ5 pro / ST80 guider setup and retail a little bit of flexibility, say when going to a dark site just taking the main tube and mount and using it visually for example.

Any thoughts? Seems like I need at least 2 new tubes and definitely not the one I have :s

[nmoushon]

The 150P I think will suit you well for mid range scope. You could jump up to a Quattro. Just compare the different FL and see what suits you better. F/4 is really nice and fast and you will be able to get more data than the F/5 for the same exposure time. But capturing extra subs to make up for the speed doesn't bother you then the 150P is fine. Also if id doesn't fit in your budget then I wouldn't bother. Especially if you are trying to save up for the RC in the future. I wouldn't get the RC now. Make sure you can master to guiding with this mid range scope so the jump to the long FL scope wont be so big. Try to aim to achieve as long of subs as you can. I would be surprised if you couldn't get at least 15min subs with that set up.

[LouisJB]

Ok, makes sense. Especially for the price. I'd stick with my 130P but there are two things, 1 is the shoddy focuser on the cheaper model and the other is the back-focus and I don't want to have to butcher it to get it to work, makes sense to sell it as a good visual scope for another starter.

As for the F4 quattro, it's interesting. I hear some people say the steel tube fast tubes can be a setup nightmare. I'd like to get from packed away to setup and imaging within 20 mins so fiddling with a fast F4 might not be the way.

So learning the ropes with prime focus guided 750mm imaging at F5 then stepping up to something like the 8" RC carbon later is probably a sensible plan.

However there is a 6" RC tube, it's tempting! But maybe a relatively wide 750mm F5 and a 1500mm RC would be complimentary whereas the 6" as a stop-gap would not be something to keep long term.

Complex isn't it! I'd also like to try and image a comet like ISON, so having something relatively wide sounds like a good starting point for many reasons.

[nmoushon]

I'd sell the 130P as is. No need to put money in it. 

It might take more than 20min to setup, especially at the beginning, but you'll soon be able to cut that down drastically. I know when I was shooting unguided with my DSLR I could be up and imaging in 10-15min. When added guiding it added another 5-10min depending on how long calibration took and if the electronics played nice. Then when I got my CCD....well haven't fully got that down yet as I'm still trying to get it all working but thats a different story. The only thing you'll have to add to that list will be collimating your telescope. You'll have to that with every scope except a refractor. You'll get that down pretty fast soon enough,if you haven't already. So when nothing goes wrong I think you'll be able to get up in imaging in 20-30min no problem....with some practice. 

ISON is actually relatively small. So you'll be able to capture it with a lot of scopes and still have a nice field of stars around it. Though the kind of wide field it sounds like your wanting with this ISON is much wider than any reflector. You need to really make sure you know what kind of FL you're getting. It sounds like your still liking the real wide field shots. Which you can only get with a small refractor and reducer or a camera lens. Which  brings up that for those wide field shots you could use a lens on your dslr thats attached to your mount. 

[LouisJB]

Hi, ok thanks.

Yes I forgot about guiding calibration. It seems to take me about 10 mins to get the mount outside and into position, put the tubes back on it and balance it and then polar align it. Then another 5-10 mins to set up the mount with 3 star align the mount focus the DSLR on a bright star etc. Then wiring up the guiding and guiding calibration seems to be another 5 mins or so.

It's an interesting point about wide-field. I have camera lenses up to 300mm at around F5 so I guess those on the guided mount could cover very wide field stuff. I think I can live with only getting parts of large objects like M31 through the telescope at the expense of getting larger views of smaller galaxies, if that makes sense.That and dropping back to camera lenses for really wide field might work ok. There aren't that many really wide field objects are there? M42 springs to mind and M45.

It also matters which sensor size I have doesn't it. I saw images from someone with an APS-C DSLR and 750mm tube and then a CCD on same tube and it appeared to 1/2 the field of view with the CCD which must be down to chip size. That chip size on a say 1500mm focal length tube would make an incredibly small field of view, too small I suspect.

In any case I can see myself with an ED80 and a 8" RC or similar in the future if this all works out as a long term hobby, it's really what direction to take for the next 6 months or a year to really learn the ropes on a range of targets. My DSLR is 16mpx but the one I hope to get is 26mpx, so a little cropping is not out of the question either.

I quite like the size of images I'm getting with the combination of 650mm 130p and 2x barlow at around 1300mm onto an aps-c sensor, not sure what that equates to image scale wise but it seemed comparable to the view through the 10mm eyepiece, so around 65x. Of course that is very slow at F10, so not workable. Also the field of view is less than 30 arc minutes (maybe 20) as I can't get the whole of the Moon or Sun in it, only about 3/4 - can't get all of M45 or M31 in either, but M42 might be a good match for it's field.

For a modest outlay it seems making progress with the 150PDS and sometimes my existing camera lenses would be a good way to progress. I saw an image of M31 from a guy at the local astronomy society using a normal camera lens (300 or 400mm ish) on an EQ mount that looked really great!

[RikM]

This is not a good image but to give you an idea of the size of the field, this is M31 with a Canon 1000D and 150P (no coma corrector, unguided on an EQ3-2 mount).

and now M45 with the same telescope and camera but on NEQ6 Pro mount.

[LouisJB]

wow, really nice! I'm certainly going to get one I think, seems hard to beat for the price. Will save the expensive RC for when I've got more experience...

Anyone want to sell their 150PDS?

[Uranium235]

Let us not forget the 130pds

 

But I think both that and the 150pds will need some sort of modding before they can do any serious imaging. Today I got my M54-T2 adapter from TS, so no more daft compression rings, safety undercuts or grub screws yayyy!

It means I can sink the CC inside the drawtube and have all-threaded connections, I will also probably claw back some focuser travel as its not intruding so far into the OTA.

But if youre thinking of an RC, skip the 6" and go for the 8" F8 model (CF). That will give you good speed (when 0.67x reduced) and binning once you get to the stage of using a CCD camera.

[LouisJB]

hi, awesome images!

both 130PDS and 150PDS I guess are very similar at F5, just the extra 15% focal length. a 130PDS would be fine, but since I have the 130P I might as well try something slightly different.

what sort of mods are you referring to, flocking and that sort of thing?

I have a camera T-thread adaper, so I'll just need the T-thread to OTA adapter of some sort, which is a T to 2" thread adapter?

Yes for the RC I was planing the 1500mm 8" carbon, but whilst I could get that now, I don't want to spend the next 3 months wondering how to get it and getting another set of accessories, I want to be able to start imaging now and learn how to do it well. Also the wider field of the F5 650/750mm will give some chance to image things too wide for the 1500 - although good point about the 0.63 reducer, so what F number would that make the RC?

[LouisJB]

Sorry, "get it" = "get it working", shame you can't edit posts....

[LouisJB]

btw, what is binned? time to RTFM I guess

[Uranium235]

hi, awesome images!

both 130PDS and 150PDS I guess are very similar at F5, just the extra 15% focal length. a 130PDS would be fine, but since I have the 130P I might as well try something slightly different.

what sort of mods are you referring to, flocking and that sort of thing?

I have a camera T-thread adaper, so I'll just need the T-thread to OTA adapter of some sort, which is a T to 2" thread adapter?

Yes for the RC I was planing the 1500mm 8" carbon, but whilst I could get that now, I don't want to spend the next 3 months wondering how to get it and getting another set of accessories, I want to be able to start imaging now and learn how to do it well. Also the wider field of the F5 650/750mm will give some chance to image things too wide for the 1500 - although good point about the 0.63 reducer, so what F number would that make the RC?

Ive yet to flock or paint the inside (got some blackboard paint), but tonight I performed surgery on my coma corrector so it could be mounted internally in the drawtube. Its now a completely threaded connection with no grub screws or compression rings (which are the cause of many ills). Its now rock-solid and has no slop in it when given a good wobble.

I found this was more or less mandatory with the weight of the camera and filter wheel I have, but it may not be suitable for DSLR use as the distance to the focal place between the t-thread on the focuser and the chip is now 47mm. I might add that if you use the baader MPCC, then surgery isnt required because it can just screw straight into the back of the M54-T2 focuser adapter (incorporates M48 thread), but you wont be getting 0.9x.

Other pending mods are to paint the drawtube black, and fit a fan and thermometer. Which is something you might  want to consider if getting a 150pds, because I seem to remember that taking a lot longer to cool down (about 45min) than this 130pds does (within 30min) - I guess it depends on whether you have time to put it out and wait for cooling (I like mine ready asap).

If your imaging camera is fairly lightweight, you might be fine with just the normal focuser grubscrews to hold the corrector and camera in place. Many a fine image has been taken with the plain-vanilla model, so just get stuck-in and get imaging! You can get more choosy about your imaging further down the line

In regard to the T2-2 inch adapter, if using a dslr and coma corrector you wont need it becuase the camera connects directly to the CC via your dslr T-ring (you need to purchase the appropriate one for your camera make). However, if running without the CC, you will need it (it connects to your camera T-ring). With a CCD I find it easier to set up since you have fewer issues because the imaging chip isnt set so far into the back of the camera like it is with a DSLR.

Look here for possible scope/camera combinations: (hours of fun!)

http://www.12dstring.me.uk/fov.htm

@Louis

Binning is a mode available to CCD chips that allows a group of (say for example) 4 pixels (2x2) to be merged into one big pixel with the (theoretically) combined sensitivity. However in reality, this gain Ive found is roughly a 1.8 - 2x gain in signal (not the 4x so often stated). Binning has a cost, it reduces your resolution by half so you either need to be operating at a medium to long focal length, or have really small pixels in your camera - otherwise you will start to get blocky stars beyond the 4" p/p sampling rate.

[LouisJB]

Great information! So the 0.9x CC that required mods to make a threaded one is the Skywatcher one? The Baader MPCC is 1x rather than 0.9? I presume the optical quality is about the same for either?

To be honest for the 1st few weeks I'll probably run without a CC - just to get the hang of it a bit better. I think I've not yet reached the image quality meaning it is that much of an issue, but once I get up and running with prime focus I expect it will be the next thing to get.

My camera is not IR modified (Pentax K5, not so easy unfortunately) so this may ultimately limit what I can do until later getting a CCD.

I tried taking an image of the Rossetta Nebula but what I saw was incredibly dim, not sure if that's down to IR/Red response or that it is very dim compared to things like M27/M31 etc.

I've set up Stellarium with my cameras chip size so I can get a feel for the image sizes of the 130 and 150pds, looks like it's a reasonable compromise between ultra wide and narrow field. M45 should fit, just. M31 will mostly but maybe not to the very edges. I can work with that.

In terms of mods, so painting the inside of the focuser with black chalkboard paint and flocking the tube will reduce stray light and improve IQ/contrast? 

My setup tends to stay in the conservatory. During the winder the temp is somewhere between outdoors and inside so I've not found extended set up times. Anyway it takes me 20mins + to get everything setup, polar alignment, star alignment, guiding so probably it has reasonable time to cool. Is that generally how it works though, longer/bigger tubes = longer cool down times?

Do you know if the 130/150PDS come with 2" to T adapter, my 130P has a T-thread on the 1.25" eyepiece holder, presume the PDS comes with something similar.

Thanks for the explanation on binning, I guess it's may be a handy option for dim objects if you have high enough resolution. My current camera is around 5k by 3.2k so maybe it would work in some cases, guess it's something you can just try out when images are dim and you want to try and extract the best image with post-processing.

Thanks for all the help.

[LouisJB]

ahah for the short term I got some longer screws and moved the primary up on my 130P. I can get prime focus on the the Moon now, hopefully that's about the same as a star i.e. all a very long way away - just need some clear skies to try it out.

Is it ok to leave the rear cover plate off? I shone a torch up from the back of the mirror cell, some light gets into the tube (not that much) but it didn't seem to affect the image. Is the mirror cell in danger from damp and the elements from the back, or so long as I keep it clean it would be ok? I could make holes in the plate for my new bolts, but at the moment it's all reversible which is good.

Hopefully I'll at least try out the setup, see how I like a 650mm field of view. It seemed pretty wide, especially after using the 2x barlow previously!

Anyway, I'll still need something with a better 2" focuser when I come to get the coma corrector, so this is just an experimentational stop gap. Now I can collminate, I'm far less worried to experiment than when I first got it.

[RikM]

Well done

You will be fine leaving the rear plate off. The newer Explorer telescopes don't even have the rear plates fitted. My 150P just has a thin bit of plastic/card covering the back of the mirror cell, my 250PX is just open. If anything it will help the mirror cool down quicker.

[LouisJB]

Thanks. It probably sounds silly but I was quite scared to fiddle with the tube to start with. Then once I got a cheshire and tried collmination I took it apart and took the mirror cell out to see how it all works. Nothing to be scared of is it really, although it all has to be handled with much care! That's good to know about the rear cover. I basically have screws like the original arrangement but longer, and the screws that pull on the cell are using wing nuts, seems massively easier to adjust - can even do it in the dark with no tools. If it wasn't for the focuser I could probably make use of this, but the cost of a decent focuser is a good chunk of the 150PDS and I could maybe sell this 130P and get the 150PDS when I'm ready for the coma corrector.

In terms of moving the mirror, if anyone wants to see a picture I'll happily post one. Not rocket science but until you've done it, it can all seem like a bit of a scary mystery.

Anyway, bit cloudy here but here is the moon in prime focus, showing it appears to be working ok.

Definitely learning, bit by bit...