Tiny chip, tiny lens?

[vlaiv]

If you have some sort of fast lens - like Samyang 135mm F/2 and plan to use it for imaging - it's worth experimenting with it for EAA as well. Some targets will probably look too small (like small galaxies and planetaries) but speed will be extraordinary.

Thing with EAA is that you want fast exposures to "start observing" target straight away, after that, all the time spent on target is just enhancement of view and law of diminishing returns kicks in. If you for example choose 4s exposures to work with (and if you have fast lens in heavy LP this is certainly plausible) - first frame will come in after 4s, and after additional 12 seconds you will have improved SNR by factor of x2 over initial impression. Next such improvement will come after 48s, and next step almost after three minutes.

If you are observing with family - this sort of "speed" helps as you need to spend only few minutes on each target - time that can be spent in analyzing progressively better image and also doing some discussion on background of the particular target (for example - observing spiral galaxy - good time to discuss galaxy types, spiral arms, mention that our galaxy also is of that type ....)

[Ags]

I don't have the TS camera lens adapter yet, so that will have to wait, but I hope I can reach focus with my 0.5x reducer and the ST80. It might work OK on the 9mm diagonal chip in the ASI178MM, and that would give F2.5 and 200mm focal length. That would give a 2.1 x 1.4 degree field. It might be nice for some larger nebulae.

What software is easiest for live stacking? Do I need to take flats? Sharpcap looks friendly, based on its website alone!

Edited June 27, 2019 by Ags

[Gina]

Yes, Sharpcap is good.

[vlaiv]

5 hours ago, Ags said:

I don't have the TS camera lens adapter yet, so that will have to wait, but I hope I can reach focus with my 0.5x reducer and the ST80. It might work OK on the 9mm diagonal chip in the ASI178MM, and that would give F2.5 and 200mm focal length. That would give a 2.1 x 1.4 degree field. It might be nice for some larger nebulae.

What software is easiest for live stacking? Do I need to take flats? Sharpcap looks friendly, based on its website alone!

I know of two pieces of software that do live stacking - SharpCap and Jocular. Second one, as far as I know - does not do capture, but rather picks up saved images and stacks them as they are written to a folder.

There seems to be no piece of software that is fully "integrated" for this purpose yet (at least I have not heard of it) - meaning you get image capture/calibration, plate solving, scope positioning, image enhancements and all the rest bits and pieces that one can think of that would be good to have in such software so we need to experiment. Actually much of EAA is still experimental.

I'm afraid that using 0.5x reducer is going to produce poor results on fast achromat - I tried it once, and while I can't recollect the details, I do remember I was not happy with results. I used GSO 1.25" 0.5x reducer with ST102. I was able to reach the focus, except - stars were not in focus - in best focus position .  Fast short achromats have loads of field curvature, adding a reducer that does not correct for this will only make things worse. I think that this lens also adds spherical (that is why I was not able to focus stars properly) in fast / curved beams.

There are couple of tips that I can offer for trying to do it:

- You might want to try reversing the lens if you have the same reducer (or one in 2" format). I've found that it works better that way and I was able to use it with small sensor and F/6 newtonian. Don't know if it is assembly error and lens is supposed to go the other way around normally and other such items are properly assembled, or if it's "universal thing".

- With such reducers reduction factor depends on distance to the chip - it goes something like 1 - distance / lens FL. To get reduction factor of 0.5 you need to place it half it's focal distance away from sensor. If you place it closer it that will lower reduction factor and possibly lessen associated aberrations, so you can play around and get suitable reduction. If you place it further, you can also achieve greater reduction. Amount of inward focus travel will depend on reduction factor - more you reduce - more you need to push assembly closer to lens, so if you hit point where you can't focus - then you can lower reduction factor.

- You might be able to use your Skymax 102 as EAA scope, but it requires some additional bits and pieces (not very expensive, but does add to total budget), however this is untested territory and I have no way of knowing if it will work. There have been some tests done of this approach that you can look at - I'll find that thread for you. Idea is to use eyepiece projection method to get reduction in slow scope. Mak is very suitable for that. Although it is slow scope - it has rather flat field over it's fully illuminated part and has one important quality - larger range of focus which is needed for this. If you manage to get something usable in terms of focal lengths (400 and below) it will be better than 80mm scope in terms of light gathering power as it is 102mm scope.

Here is that thread:

All calibration files help, but are not needed - it will produce same effect like not using them in regular AP, but might be less noticeable because achieved SNR will be lower due to shorter observing time. If you can - do both darks and flats / flat darks, but if not - don't worry about that.

[Ags]

Sharpcap downloaded and I have even done my first session of live stacking - admittedly of my own face using my laptop's webcam, but you've got to start somewhere right? I dropped quite a lot of frames trying to stack at 30fps or whatever 😃

Anyway Sharpcap looks fairly straightforward. 

@vlaiv I doubt the 0.5 reducer will work in the ST80 but I will see soon enough. It certainly doesn't work with eyepieces in that scope. The reducer does work well enough with eyepieces (for deep sky, not planets) in the Skymax so it might be an option there.

On the subject of EOS-ZWO adapters, this looks interesting:

https://www.teleskop-express.de/shop/product_info.php/language/en/info/p10451_Canon-EOS-Objektivadapter-mit-Filterschublade-fuer-Astro-Kameras-ZWO--QHY--ATIK----.html

Edited June 27, 2019 by Ags

[Ags]

I tried the 0.5 reducer with the ST80 last night and all manner of weirdness resulted.  Used in the combination of ST80 -- Wratten #8 -- 0.5 Reducer -- ASI178MM, I could just reach focus but had enormous halos around all stars. I tried removing the halos by removing the Wratten #8, but the weirdest thing happened. Without the color filter, the stars no longer came to a focus - instead they focused as thin rings (black in the middle). 

[Gina]

Any filter or even plain glass will increase the focal distance, usually by one third of the thickness.

[Ags]

I get that, but I don't get how the reducer then focused the stars into rings...?

[Gina]

That's what you get with out-of-focus point light sources.

[SIDO]

Using less focal reduction provides better images when using my st80 with asi385, I removed the reducer from it's case and inserted it in the camera's nosepiece...It's held there by two set rings that allow for adjustment within the length of it's internal threading.

Easy way to adjust or finetune reduction or achieve focus.

                         Freddie...

Edited July 1, 2019 by SIDO

[Ags]

7 minutes ago, Gina said:

That's what you get with out-of-focus point light sources.

Not with refractors - you get a smooth bokeh disc. With a mak you get a shadow of the central obstruction, but I was using a 'frac and the image looked nothing like that.

[Gina]

Ah yes - OK.

[wimvb]

3 hours ago, Gina said:

That's what you get with out-of-focus point light sources.

 

3 hours ago, Ags said:

Not with refractors - you get a smooth bokeh disc. With a mak you get a shadow of the central obstruction, but I was using a 'frac and the image looked nothing like that.

Actually, the psf of a defocused star can have a dark centre even for a refractor at the right amount of defocus. Theoretically, that is.

https://en.m.wikipedia.org/wiki/Airy_disk#/media/File%3ASpherical-aberration-slice.jpg

 

[Ags]

7 hours ago, SIDO said:

It's held there by two set rings

Do you have a link to this product? I've never seen anything like that before?

[SIDO]

48 minutes ago, Ags said:

Do you have a link to this product? I've never seen anything like that before?

These are just the set rings that hold common 1.25 filters or reducers in place, just the threaded ring with 2 digits on one side. Just make sure to face those digits outward and away from the reducer.  Your reducer has one of these threaded rings holding it in it's case, I borrowed my second one from a cheap #12 filter that I had laying about.

 

 

 

 

[SIDO]

4 hours ago, wimvb said:

 

Actually, the psf of a defocused star can have a dark centre even for a refractor at the right amount of defocus. Theoretically, that is.

https://en.m.wikipedia.org/wiki/Airy_disk#/media/File%3ASpherical-aberration-slice.jpg

 

I have seen this with my st80 and reducer...

[Stub Mandrel]

5 hours ago, wimvb said:

 

Actually, the psf of a defocused star can have a dark centre even for a refractor at the right amount of defocus. Theoretically, that is.

https://en.m.wikipedia.org/wiki/Airy_disk#/media/File%3ASpherical-aberration-slice.jpg

 

On Friday night my 135mm lens drifted out of focus and the stars slowly morphed into doughnuts, luckily I spotted it and didn't lose too many subs.

[wimvb]

3 hours ago, SIDO said:

I have seen this with my st80 and reducer...

 

1 hour ago, Stub Mandrel said:

On Friday night my 135mm lens drifted out of focus and the stars slowly morphed into doughnuts, luckily I spotted it and didn't lose too many subs.

Isn't it nice when theory works?