SharpCap Forums

M35 + NGC 2158
using a technique I developed for imaging Open Star Clusters described here: https://snrcalc.now.sh/help/open-star-clusters

Captured over three sessions

Session 1:
January 12, 2020
L 540x15s bin1
93% Moon 50 degrees away. Below horizon at start. 15 degrees above horizon at end. Estimate change in Bortle class from 5 to 7.

Session 2:
January 15, 2020
R 180x14.3s bin2
G 180x8.4s bin2
B 180x13.0s bin2
Moon below horizon. Bortle class 5.

Session 3:
January 17, 2020
R 120x14.3s bin2
G 120x8.4s bin2
B 120x13.0s bin2
Moon below horizon. Bortle class 5.

William Optics 71mm f/5.9
Atik 314E (Read Noise: 5.3e-)
Optolong LRGB filters

Image quality suffered somewhat due to under-sampling. The Atik 314E really does need a longer focal length scope.

Nevertheless pretty impressive for a "noisy" CCD camera.

Lovely!

Brian

Good differentiation between the 2 types of clusters. I make that about 5 hours of integration?

Dave

Thanks, Minos and Dave.

I've always wanted to image these clusters side-by-side. Great color differential. Large magnitude difference. In hindsight I should have lowered the exposure a tad more. Some of the bright blue stars saturated. I determined the exposure when the cluster was entering target range. I must remember that the atmosphere is thicker there. As the cluster rose higher the atmosphere grew thinner and stars became brighter which caused saturation.

Nearly 5 hours 15 minutes, and a couple hours of processing time in APP. That's what it takes to get a bright, high signal-to-noise ratio image. I think next cluster I do I'll use bin1 for RGB instead of bin2. My camera is already under-sampling at bin1 so bin2 is worse.

Brian

oopfan wrote: ↑Mon Feb 10, 2020 8:31 pm Some of the bright blue stars saturated.

That's to be expected from your doublet. Would you consider using a Baader Contrast booster to mitigate the unfocused blue spectrum?

Thanks, Minos. I'll look into it.

I think what I need is a true APO. The manufacturer marketed my refractor as APO-like but I'm not the first to complain about the lack of blue performance. People on CN have criticized this particular model. Go figure that I should learn about it after making the purchase.

I'm leaning more towards an 8-inch f/3.9 Newt. I've never owned a reflector. I like the diffraction spikes.

Brian

Brian, I too have struggled with the woes of chromatic aberrations inherent in doublets, triplet and quads...so much so, that I decided to completely revamp my imaging system to a 130pds reflector with a small enough sensor (asi290) so as to negate the need for a coma corrector and have absolutely no refractive elements in the optical train!!

It's working well for me so far, but I'm restricted to a small fov (obviously ) and I'm currently looking into coma correctors (i.e. 3-element maxfield) for a larger sensor (i.e. asi533mc or Altair 269c or something), but that is far away. I'm currently happy with using my 290 color and mono for zero chromatic aberration imaging.

Having said that, these filters do help, but not as much as a good triplet. I really liked my esprit80 and would buy it again in a heartbeat..if I could afford it.

Minos,

Is this what you have?

https://www.firstlightoptics.com/reflec ... s-ota.html

Great price! Perfect focal length for my Atik 314E.
Weighs 9 pounds. My mount can easily swing it.

Question: Where do you mount your guide scope?

Thanks,
Brian

Yes it is and I ordered it from FLO back in march I think. It arrived here on long island in 2-3 days with dhl iirc. It's a wonderful telescope and superb value for money, so much so that I own two ( one in Cyprus for when I go back home for holidays). Here's how I mount the guidescope.

Minos,

Only 200 euros for a major boost in performance.

I just finished modeling it in my software. Given M51 Whirlpool Galaxy and a target SNR of 25, which puts you in IOTD territory, the comparison is as follows:

Skywatcher 130mm f/5: 194x120s = 6.44 hours
William Optics 71mm f/5.9: 236x120s = 7.84 hours

Therefore:
1.5 hours reduction in total integration time
No more chromatic aberration
No more under-sampling

I might seriously consider this. It looks like it is only available in the UK and Europe. I tried OPTCORP in California. They carry SkyWatcher but not that model.

Brian