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Going against good advice...


parallaxerr

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I started my journey into AP a few months ago having been pointed in the direction of the “no EQ DSO challenge” thread. As I already owned equipment on a par with some of the members of that thread, I soon found that I was getting some good results in un-guided Alt/Az imaging.

My current setup consists of a Nikon D3200 DSLR attached to a William Optics Zenithstar 66SD refractor on a Celestron Nexstar SE Alt/Az mount. I’m sure if I’d asked the question at the time “is this gear any good for AP”, then the replies would have been a resounding no. However, thanks to some encouragement from forum members, I decided to have a go. The only thing I added was a Baader coma corrector which is a reasonable match the ZS66SD, in light of the lack of availability of the original matched WO flattener.

Alt/az imaging is of course a challenge with field rotation and subsequent altitude limitations being the main factors. This means we are restricted to shorter subs, generally 30s in my case and often have to image at low altitude to the East or West which helps negate field rotation somewhat, but does mean we’re often peering through heavy LP. Despite this, members here are producing some really quite remarkable images. I am very pleased with my latest attempt which is M33 imaged over 3 nights with about 6hrs of data. I actually had around 50° rotation in my image stack, but thanks to a large FOV I could crop it all out on this small target.

6hr v1.1Gimp.jpg

But, there’s no doubt there’s a limit to this method and I keep making the mistake of looking at images taken with EQ rigs. Having seen an M33 image from an EQ mounted scope, I realised how much more there was to be captured. Reading Joseph Ashleys book titled “Astrophotography on the go” raised an issue I hadn’t previously considered, that being that despite the short subs, Alt/Az images still suffer from field rotation at pixel level which accounts for their softer look.

This is where I’ve gone against the good advice. Put simply, there’s no way I can shell out for a decent EQ mount for some time. I considered the EQ3 Pro Synscan as good results can be had with it but really wanted to stick with a Celestron because I like the software, the cheapest option being the AVX (notwithstanding used items). Instead, for just 30% of the cost of the AVX, I have purchased the new Celestron wedge for Nexstar SE/Evolution mounts.

It’s not that I have personally been advised against this piece of equipment, but reading older threads, when the Nexstar SE was still in its prime, it’s clear that some people struggled to get the results they wanted due mainly to the unbalanced single fork arm geometry, some did produce good results though it must be said. There is one major difference between those setups and mine though and that’s the scope. Every wedge mounted Nexstar imaging thread I’ve read involves using the supplied C8 OTA with a FL of 2032mm, loaded with autoguiders and other accessories pushing the mount and guiding to its limits, with owners expecting no less than 5min subs. Instead, I will be un-guided with just 4-5lbs of tiny refractor with a FL of only 388mm and DSLR attached, if I can double my signal using 60s subs un-guided and reduce the pixel level field rotation, thus sharpening up my images, I’ll be a happy boy.

So, watch this space. It may well turn out to be a complete waste of money in which case feel free to mock my decision, but I’m quietly confident that this may give me my first little taste of EQ imaging, without shelling out the big bucks!

Anyone here using a setup remotely similar?

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Wirh the short fl you are using, you should be able to get double the exposure time without guiding. Just get the balance and polar alignment correct.

Btw to double the snr, you need four times the exposure time (scales as square root).

Good luck with this setup.

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There are several messages in your post. Can you make good images with non-optimal kit? Of course you can. You demonstrate this. Should those of us asked for advice about what is the optimal kit recommend non-optimal kit? Of course not. That would be absurd. 

Olly

 

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49 minutes ago, ollypenrice said:

Should those of us asked for advice about what is the optimal kit recommend non-optimal kit? Of course not. That would be absurd. 

That's not the message I was trying to convey. This is just about doing what you can with what you've got, or in this case improving what you've got with as little extra expenditure as possible! 

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3 minutes ago, parallaxerr said:

That's not the message I was trying to convey. This is just about doing what you can with what you've got, or in this case with as little extra expenditure as possible! 

..which is, of course, perfectly fine! I'm all for it.

Olly

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It's arrived :icon_biggrin: All credit to Microglobe & DPD, I ordered this yesterday after lunch and it just arrived.

What a lump! Much larger and heavier than I was expecting and the fit and finish of the machined parts looks/feels very good. Both the Dec and RA adjusters feel smooth, running on nylon shims. 

Now I've got to get it in the house under the radar! Hopefully once it's fitted, SWMBO won't notice the mount looks "wonky"!

20161220_111754.jpg

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21 hours ago, parallaxerr said:

the replies would have been a resounding no

Maybe we should be a little more careful with what we recommend? The old school ed80-on-eq6-minumum-plus-another-thousand-or-so-for-guiding days are thankfully gone and at last we are seeing results which reflect [1] this. 20 years on, we now have a choice:)

[1] not intentionally

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For me it's all about expectations and the sorts of images you want to achieve. Sure you can do it with kit that isn't 'recommended', of course you can...... but what is it you exactly want to achieve? If you want images of the highest quality comparable with the best imagers on here, then I'm afraid that my recommendations would at this moment stay the same.

I see images taken with kit that isn't generally recommended and while I admire the effort that people are putting into getting the images and when all is considered they are very accomplished..... for me they are not of the quality I'd want to be aspiring to.

I'm not knocking anyone and the kit they have nor the effort that they put in, I'm not saying that if you can't afford a few ££'s then you can't 'do' AP (that is clearly rubbish), but if you want to aspire to be imaging with the very best, then you will benefit hugely from the 'oft recommended' kit... in my opinion of course.

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6 minutes ago, alacant said:

Maybe we should be a little more careful with what we recommend? The old school ed80-on-eq6-minumum-plus-another-thousand-or-so-for-guiding days are thankfully gone and at last we are seeing results which reflect [1] this.

[1] not intentionally

I think it's a fine balance between Ollys point above and yours. It would be bad advice to suggest buying the equipment I'm using to a first time imager, in which case an EQ would be better. However, if someone already owns equipment suitable for Alt/az imaging and/or there's a budget restriction, then they shoudn't be discouraged from having a go.

3 minutes ago, swag72 said:

I'm not saying that if you can't afford a few ££'s then you can't 'do' AP (that is clearly rubbish), but if you want to aspire to be imaging with the very best, then you will benefit hugely from the 'oft recommended' kit

Agreed. It is important to limit ones expectations when using "lesser" equipment.

Anyway, it will be an interesting experiment for me to see if I can visibly improve my images by using the wedge. Given that the worst backlash in the SE mount is in the Alt axis, hopefully it will perform OK on the wedge in RA, where the alt/dec axis has less to do. The latest firmware also gives me the All Star Polar Alignment method which doesn't require visibility of Polaris and claims better alignment accuracy when using a star closer to the Meridian and Celestial Equator, which is a bonus in my East to West through South available sky.

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Good luck with the wedge. Hopefully it is compatible with the mount's software. If your alt axis has backlash, this will now be in your ra axis. Some gentle imbalance can improve this, but you should check if is possible to adjust the mount to remove the backlash.

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Yes I have the latest software installed which has EQ and all star polar align routines. I got it all together, not without issues though. First off I had problems getting the wedge attached to the tripod due to paint in the wedge threads so had to clear them out and use a bit of grease.

The second issue came once the the mount was fitted, I tried rotating the RA axis only for it to come to a grinding stop after a few degrees. Turns out the supplied bolts are too long and run through the mount base and into contact with the AZ/RA motor pinion gear! I now have a few damaged teeth on the brass gear, fortunately not where it meshes with the crown gear. A quick google search suggests I'm not the first to experience this, major fail there Celestron. I had to fit spacers about 6mm thick to overcome this, so Celestron got their dimensions very wrong. It all appears to be OK now though, fingers crossed the motor is OK.

20161220_190117.jpg

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That certainly is a major design flaw from Celestron. The setup looks nice, I hope it performs well in the field. If you level the mount and set the Alt of the wedge to your latitude, polar alignment will be easier and repeatable. (You probably already knew that.)

(BTW, you seem to have forgotten to load your battery charger. :wink: )

Cheers,

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First bit of action with the wedge tonight now we finally have clear skies. I have been reading the Nexstar SE EQ North Align and All Star Polar Alignment methods over and over waiting to try them out. Also I started reading about drift aligning and was all set to give it ago when I discovered Drift Alignment by Robert Vice (DARV) which uses the DSLR to expose alignment drift.

Anyway, I set up tonight and carried out an EQ North align on Enif & Capella which have nice separation, followed by Polar Align on Menkar which was close to the meridian/equator intersection. I then cycled power and did another EQ North align to get my alignment error, which the mount reported as 30 or so arc seconds on both axes. Not bad for a first attempt. I went straight on to drift aligning then and, blow me, it was bang on near as damn it. Now, I only used a 125s exposure on each axes as it was my first attempt, so there's room for improvement but I'm very happy with the result. The Celestron ASPA is obviously quite accurate on it's own - alignment frames below, Menkar & Betelgeuse.

 

 

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