Wide Field EAA Video Tutorial

[curtisca17]

I want to share a video tutorial I just posted on EEVA with a wide field scope.  I made this at a recent star party using a Sharpstar 61 EDPH III wide field refractor I just bought on a Skywatcher AZ GTi mount I borrowed from a friend.  I also bought an ASI858 color camera to go with this setup.  In the video I explain my choice of equipment and point out some alternative scopes and cameras that will also work well.  I also walk through the setup step by step and finish with a short live stacking demonstration of M31, M33, the Eagle nebula and others using Sharpcap.   The objective is to show what can be done with a simple, light weight, moderately priced setup using a refractor and camera with a FOV of roughly 1 x 2 degrees.  https://www.youtube.com/watch?v=h8cXY4mUBng

Hopefully folks find this useful.  As always I appreciate feedback so I can do better next time.

Regards,

Curtis

[Franklin]

Thanks for another informative video. I intend giving EAA a go this coming season with a Vixen ED70SS and Altair183c hypercam.

[curtisca17]

Thanks.  You should have fun with that setup.

[PeterC65]

Another useful video tutorial. Thanks for putting it together Curtis.

I use a TS Optics 72mm F6.0 Apo refractor with a Uranus-C (IMX585) camera for widefield EAA, but currently without a field flattener. Do you think a field flattener is important for EAA?

 

[Franklin]

12 minutes ago, PeterC65 said:

Do you think a field flattener is important for EAA?

 

That's a question I'm interested in hearing the answer to. I have a flattener/reducer for my SD81 but am unsure of the distance to sensor when setting it up or indeed if it is needed at all for simple EAA. I guess the reducer would shorten exposure time at the expense of image size but the flattener seems more appropriate to proper imaging which is something I'm not wanting to get in to at present. The little ED70 came with a reducer as well but am unsure of it's use also. My intention is to try a very simplified approach to EAA, just a camera linked to a laptop to give a live view on targets rather than straight visual through the eyepiece. So far I've got a finder eyepiece(30mm plossl) parfocal with the camera on a flip-mirror. I am confident that with my small setup, ED70 on AP with tracking, I will be able to locate objects of interest and get them in focus on the laptop screen but am totally unsure on stacking frames, applying calibration frames and post processing. To be honest I'm not really interested in creating a nice image to save and will probably just keep a record of my EAA observations by taking a screen-shot of the live view image. Now the darker nights are on their way I just need some clear sky to get out and experiment I guess. If I have any success I will then try putting the camera on the big refractor and the goto GEM, maybe even try to get it semi-automated so I can view my laptop from the comfort indoors? That, for me, would be an achievement in itself.

[curtisca17]

A field flattener is certainly useful for traditional astrophotography which I also do and is why I paid the additional $199 to get it with the OTA.  That is because astrophotography is all about getting the best looking images one can get all the way to the edge of the field of view.  EAA is a different animal.  Primarily the objective is to be able to see much more than we can with an eyepiece but not have to go through all the work required to get a astro-photograph.   10 years ago it was common to use video cameras for EAA which had very large pixels ( 8 - 9 microns) which produced blocky looking stars with much less resolution than we get with today's CMOS cameras using 4 micron and smaller pixels.  It was also very common to buy very inexpensive 5X reducers, essentially binocular objectives, use a back focus distance longer than the reducer was designed for to get a higher reduction factor or combine multiple focal reducers to get greater reduction.  All of these things meant that we did not have great looking images across the entire field of view.  But we were excited and happy to the advantages in speed that these gave us so we could see more in real time.

EAA has evolved.  I think most folks have put their video cameras on the shelf and are using the latest CMOS cameras.  We do dark frame subtraction on the fly.  And some do flat field correction on the fly.  Both essential techniques for traditional astrophotography.  Others pay extra for cooled cameras to beat back underlying noise even more.  So too do many use field flatteners and coma correctors to improve the views.  EAA has almost become astrophotography light where we not only expect to see many DSOs in real time throughout a night of viewing, but we expect them to have much of the image quality of astro-photos.  

So, is a field flattener an essential tool for EAA?  In my opinion it is not any more than a cooled camera and other extras are.  It comes down to personal preferences and personal budgets.  If you want the best looking image possible then you will add these extras if you can afford them.  If you do not have them you will likely still enjoy EAA views many times better than what we were excited to see 10 or more years ago with the equipment available to us.

 

As far as the spacing for the reducer for your SD81, typically the spacing on focal reducers for refractors is 55mm but you should confirm that with the manufacturer of the focal reducer.  55mm is common because it works universally for DSLRs with adapter rings.  55mm is not the typical spacing for focal reducers for SCT like the Celestron 6.3X and 7X reducers where the spacing is 105mm for both.

Regards,

Curtis

[PeterC65]

I do have a field flattener which is also a x0.6 focal reducer. I have been using this with the 72mm refractor to get a wider field of view. The back focus is setup correctly (55mm) but I find that it doesn't give me a flat field. That may be because it is doing x0.6 reduction or because it is a generic flattener / reducer and not one specifically designed for my refractor. Looking at the edge stars, and doing some research, it looks like I don't have enough back focus so one of my things to try is to increase the back focus a little.

What made me wonder about the usefulness of a field flattener was when I bought the Askar FMA135 which has a built in field flattener. The images from that are dead flat, and very impressive, and it is now my goto setup for widefield. I can get a generic x1.0 flattener for the 72mm refractor and that is what I'm considering. If I look carefully at the edge stars without a field flattener they are distorted a little, but I have to look quite hard to notice.

@Franklin, I'd recommend you do live stacking (with SharpCap) even for simple case EAA. I don't capture flats and have only recently started capturing darks, which I think do make an improvement and are easy to do with SharpCap.