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 Post subject: IR/UV cutoff
 Post Posted: Fri Sep 29, 2017 5:18 pm 
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I have a ASI1600-mm cool with the LRGB and narrowband filters I bought about 6 months ago and I have a couple questions.
1) Is is necessary to use a UV/IR cutoff filter in front of the individual RGB or narrowband filters?

2) I am also getting a lot of purple finging when using the 1600mm-cool that I didn't get using my Canon DSLR. The telescope is the same, its an Explore Scientific ES 127 APO. Orion was taken with the 127 APO and a Cannon with M13 was recently done with the ES127 and the ASI1600-mm cool. I do have trouble getting a good focus with the blue filter. Usually with the L, R and G filter I can get around a 2-3 on Half Flux radius but the blue is usually 3-4 even with trying to refocus. Could there be an issue with the blue filter? Thanks.


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 Post subject: Re: IR/UV cutoff
 Post Posted: Sat Sep 30, 2017 1:51 am 
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the RGB and narrow banding filter already cut IR and UV
so you can imaging with R G B L or even without L

about blue problem, maybe just because of seeing
blue light is more easier affected by seeing

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 Post subject: Re: IR/UV cutoff
 Post Posted: Sun Oct 01, 2017 2:39 pm 
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Sam,
I looked into my blue fringing issues and i do recall in my notes that I can gain a better focus on the green and red filters versus the blue and lum filter. The narrowbands also focus much tighter. How sensitive is the ASI1600 to the IR spectrum? I am thinking that the cutoff point of the IR and Blue filters in the RGB set let just a little too much below 400 nm or such through and starts to bloat the stars. Several weeks ago I spent some time calibrating the focus on each filter to check offsets for autofocus, the ability to get sharper focus for the L and B filters were by far worse than the G and R. The air temp was the same as were the seeing conditions and same time of night. I am thinking an IR/UV cutoff is needed to block light below 400-420 to improve the lower end performance of the camera.

In the end I think my blue fringing is a simple result of fatter stars across the blue and L filter vs the red and green. That would also explain why this fringing shows up on this camera and not my dslr which is unmodified. Thoughts?


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 Post subject: Re: IR/UV cutoff
 Post Posted: Mon Oct 02, 2017 12:26 am 
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Location: St Leonards, Vic, Australia
I use a FULL full modded Canon 1000D in spectroscopy, and find I can record down to around 365nm.
Yes, focusing in the UV is difficult and the focal point can be mm from the green focus.
Try adding a UV-IR filter and see if it makes any difference.

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 Post subject: Re: IR/UV cutoff
 Post Posted: Tue Oct 03, 2017 1:18 pm 
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If I were to use a 2" UV/IR cutoff filter like the one you sell, where would it fit in the optics train. I have the AS1600mm-cool ==>Filter wheel==>OAG==>focal reducer

I don't see a good location to attach this. Would a 1.25" filter work better, somehow?


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 Post subject: Re: IR/UV cutoff
 Post Posted: Thu Oct 05, 2017 3:18 am 
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arbydog wrote:
If I were to use a 2" UV/IR cutoff filter like the one you sell, where would it fit in the optics train. I have the AS1600mm-cool ==>Filter wheel==>OAG==>focal reducer

I don't see a good location to attach this. Would a 1.25" filter work better, somehow?


why do you need 2“ cut filter if you already have the filter wheel

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 Post subject: Re: IR/UV cutoff
 Post Posted: Thu Oct 05, 2017 12:26 pm 
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Sam wrote:
arbydog wrote:
If I were to use a 2" UV/IR cutoff filter like the one you sell, where would it fit in the optics train. I have the AS1600mm-cool ==>Filter wheel==>OAG==>focal reducer

I don't see a good location to attach this. Would a 1.25" filter work better, somehow?


why do you need 2“ cut filter if you already have the filter wheel


Sam,
I am getting significant bloating on the blue and luminance filters even after refocusing. The Baader UV/IR cutoff I plan to use cuts off about 410nm where the ZWO goes down to 380. I am hoping that will help tighten up the starts in the blue and luminance channels.


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 Post subject: Re: IR/UV cutoff
 Post Posted: Thu Oct 19, 2017 8:53 pm 
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Hi

I'm getting the exact same thing using a Televue Pronto refractor and the ASI1600MM-cool with the ZWO LRGB filter set. But I don't get it with a Maksutov telescope and a SCT.

The refractor images through the R and G filters have nice small stars - even the bright ones, but the L and B images have stars that are easily twice the size of the R and G. I think the underlying problem is that our refractors are optimized in the visual range of colors and wavelengths below 400nm are not well corrected. The new ZWO filter set for the ASI1600 cuts off at 380 nm. The reason you can't refocus to take care of the blue may be that the telescope may have a different focus point for blue close to 480 nm than blue close to 380 nm.

If you look at other manufacturers that have filters specifically designed to reduce the bloated stars in the blue/UV range they mostly cut off at 420. Even the other ZWO UV cutoff filters cut off at 400nm.

Though it isn't very useful for tri-color imaging I took some test exposures with a Lumicon 2" Deep Sky filter. It allows light to pass from 450nm to about 540nm. The stars were very sharp.

So I wish that ZWO had a version of the protect window that had a transmission like the D25 IR-CUT protect window designed for other camera models. So perhaps a question to Sam would be, could a commonly available sized 31mm filter work in place of the 32 mm filter found on the ASI1600MM?

After the clouds pass I'm going to try a 2" Baader UV/IR cut placed on the telescope side of the reducer/corrector and use the ZWO filters in their normal place between the camera and reducer/corrector and see if that helps. I'll let you know.

Hans


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 Post subject: Re: IR/UV cutoff
 Post Posted: Tue Nov 14, 2017 7:40 pm 
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Location: Oslo & Jotunheimen, Norway
hansdemoor wrote:
... So I wish that ZWO had a version of the protect window that had a transmission like the D25 IR-CUT protect window designed for other camera models. So perhaps a question to Sam would be, could a commonly available sized 31mm filter work in place of the 32 mm filter found on the ASI1600MM? ...

+1
From the curve of the D21 IR-cut protect window, this seems to correspond to the Astronomik L2 which is a good match for the very good, but not perfectly "color-free" optics.

Why not an IR/UV block version of the ASI294/ASI1600 sized D32 AR protect window?

I can't think of any reason, within my use, where it would be wrong to have IR/UV-cut "permanently" placed. (I have IR-pass filters and other fun stuff for my mono cams)
Maybe an "emergency" at a wrong spot, using an LPS filter like CLS/P2/D1, but I figure that some extra IR/UV-cutoff wouldn't harm..

I'm currently having Gerd Neumann at Astronomik make me a special adapter for their 31mm filters, but I would simply prefer an IR/UV-cut protect window upgrade.

Edit:
Sam; if an IR/UV-cut protect window is NOT anywhere near for the ASI294 (or 1600), could you please provide me with the exact measurement requirements of the 294 window? Diameter 32.0mm and 2.0mm thick? Or would 1.1mm thickness do? (maybe add a new gasket)
Thanks :)

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CGEM-DX, AZ-EQ6 x2, C11HD/.7red/Hyperstar, TS-APO130 flat/red, TS-Star71, ASI1600MMC + EFWmini w/CLS-RGB-Ha, ASI1600MMC + EFW w/CLS-LRGB-Ha-O3-S2, ASI294MCPro, ASI290MM + EFW w/LRGB+IR642+IR742+IR807+U+CH4, SmartEQpro, EOS5D2-mod & ++lenses.


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 Post subject: Re: IR/UV cutoff
 Post Posted: Wed Nov 15, 2017 1:11 pm 
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you can use one 1.25" filter on the 294 with the help of 1.25-T2 adapter

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