performance of Z70 + WO Flat2

orly_andico · Post by **orly_andico** » Thu Feb 03, 2011 5:56 pm

hi all

I'm currently not in any position to upgrade my astrophotography kit. Not to mention I haven't even gotten to using my existing gear "in anger" due to the bad weather and light pollution.

Anyway here is a single shot I took (30 seconds) of M45 with a Pentax K20D. This has been contrast-stretched and I adjusted the red component, there was far too much red, probably a white balance issue.

Entire image:

Center @ 100% (note this is a 15 megapixel APS-C sensor):

Extreme left edge @ 100%:

The performance with the Flat-2 is much, much better than without it (here's an unflattened image for comparison that I took in Punggai last August)

My question is... how much better can things get? say if I get a triplet or the Astro-Tech ED 65 Quad?

It seems to me that the performance of the Z70 + Flat-2 right now exceeds my skills already, but am thinking about the future.

timatworksg · Post by **timatworksg** » Thu Feb 03, 2011 6:37 pm

I'm not familiar with the Pentax but can you take RAW files? Even if so, the original exposure plays a part and there is so much one can do with a RAW file if the original exposure didn't come out as planned.

If your having light pollution, one problem even I face with my ZS66 is due it being a small scope, the nearby street light glow creeps in easily compared with a larger scope. The Flat2 has done a reasonable job!

Did you use any Dark Frames? They really help! Take a few Dark Frames and Average them or Sigma combine. Then subtract.
I would not so much contrast stretch but open the stacked/image file in PS and using levels, select a black point with the dark black eyedropper. This sets the black point. Then adjust the Histogram so that the left arrow (blk point) sits just before the left side of the histogram. The right arrow (white point) should be at the right most point of the Histogram. If you have broken lines at right, you may have to sit the arrow somewhere in between, so you don't blow out or oversaturate the white! Use the middle (mid point) and adjust to just about bring the whole image out, but not overdoing it! Then OK, rinse and repeat, rinse and repeat.
You could also apply a screen layer after Levels adjustments. Duplicate the layer and select SCREEN. The image will become brighter. Then adjust opacity/Fill of the layer. A little at a time. You can stack multiple SCREEN layers to slowly boost the contrast.

One prob I find with DSLR's or consumer cams is it's wonderful ability to pick up ambient glow all over! I find they pick up this easier then a dedicated CCD cam. Don't you have a MEade DSI?

I have serious light pollution from my 2nd floor balcony. So i have to really time my AP sessions. I start tracking early and wait till the target is just away from LP. Then I start exposing. I take ALOT! So I have a nice choice of what I can stack. When I have to shoot SOuthwards, I have to wait for the target to be above more and away from a street lamp before I can start exposure.

White balance does play a part in the camera's processing. You can also use lower ISO (400/800) but expose longer. Test shots can help! It's a compromise in trying to grab more and risk more LP or expose less and loose LP. I had lots of LP when I used my DSLR at ISO800 but much less at ISO400, but loose on stars. No issues with a dedicated CCD cam, but as any hobby, take your time and try. take notes and be patient. I missed out alot of targets! But I make do with what I can really take. Sometimes it's a easier.
Getting a larger or better scope does help somewhat. But it will still come down to having what you have and making the most of it! Keep trying...one day something will work and then you can build on that! When I started, I made TONS of mistakes and everything turned out terrible! Keep at it...!!

orly_andico · Post by **orly_andico** » Thu Feb 03, 2011 7:20 pm

hi Tim

that's a single shot only, no flats, no darks. I am only eliciting comments on the optical performance of this combination in terms of field curvature and CA on bright stars. if i stacked etc. those factors might be masked.

i'm only gonna use the DSI for guiding because the chip is so small, you can't even fit M42 on it. i will be using my Canon DSLR for astro going forward though, it has much nicer noise characteristics than the Pentax.

timatworksg · Post by **timatworksg** » Thu Feb 03, 2011 7:32 pm

Hi Orly,

Oops...my bad then. Got carried away with the methods. Guess I should look more. Sorry.

In that case, optically it's a step forward!! The Flat2 really helps tons!! With the comparison it's a huge difference in performance.
Yeah the DSI makes a better guider then imager. Sad they stopped the DSI III!
Since you have the Canon...lots can be done! Great!

orly_andico · Post by **orly_andico** » Thu Feb 03, 2011 8:41 pm

Because I am only using a GP, I don't intend to use a bigger scope. Maybe a Megrez 90 eventually and demote the Z70 to guider. Or, find a WO66 and use that as a guider.. aperture isn't that big a deal when imaging anyway, so the lighter the better.

Something that piques my curiosity.. how much "better" would things be if I used the FS60 + its dedicated flattener. That's really the point of my post... can I get really pinpoint stars to the edge with one of those premium tubes, or not?

cloud_cover · Post by **cloud_cover** » Thu Feb 03, 2011 11:54 pm

Orly, that flattened edge does look pretty good anyway

Post by **Airconvent** » Sat Feb 05, 2011 1:51 pm

I am not too sure about the colours but have you considered the Pentax k-x? Its based on a low noise sensor which would be ideal for astrophotgraphy. Best to get the K5 but if you are on a budget, a K-x is very afforable now especially a second hand one. otherwise pay a liitle more for the K-r.
Nice effort in anycase! [smilie=cute.gif]

orly_andico · Post by **orly_andico** » Sat Feb 05, 2011 2:44 pm

hi Richard,

I would've gotten the K-x except for two things:

1) cannot go over 30 seconds without dark frame subtraction

2) the AF performance is lacking with the 100mm Macro

So the 40D I'm using now, works very well with the Canon 100mm Macro, and works fine for astro as well. Not to mention, it costs about the same as a K-x used.

I still kept my K20D because it's weather proof and the in-body stabilization is handy. But for astro, the K20D absolutely sucks! (I already did the debug mode thing to turn off DFS)

orly_andico · Post by **orly_andico** » Sat Feb 05, 2011 2:50 pm

This is 7.5 minutes from my balcony, Canon 40D (in RAW this time!) with 5 darks and 5 flats. Focused on a star about 30% out of the center. Also used Pixinsight to get rid of some of the sky gradient (wasn't able to get rid of everything though)