10 replies to this topic

[Poynting]

Hello,

 

I recently purchased a used TS-100Q scope. I had first light last night and noticed quite large bloating in my blue channel, using an ASI2600MC. Is this normal for such a scope? Any experiences appreciated, as I am kind of new to large refractors for imaging. It is a quadruplet with a supposed FPL-53 element.

 

[Der_Pit]

Yes, refractors and blue/UV don't go together well.  Refractive index - and thus also focus -  changes fast there.  So a UV cutoff filter is highly recommended, and best one with a higher blue cutoff.  I'd use something like an Astronomik L2 or L3 filter, as I don't have light pollution, maybe others can recommend specific LP filters with higher blue cutoff if that is an issue for you.

[Poynting]

Yes, refractors and blue/UV don't go together well.  Refractive index - and thus also focus -  changes fast there.  So a UV cutoff filter is highly recommended, and best one with a higher blue cutoff.  I'd use something like an Astronomik L2 or L3 filter, as I don't have light pollution, maybe others can recommend specific LP filters with higher blue cutoff if that is an issue for you.

Wow, I had no idea I would need one of those. I thought my ASI2600 had a sufficient filter on the window, but perhaps that is only effective for IR Cut.

[Der_Pit]

Wow, I had no idea I would need one of those. I thought my ASI2600 had a sufficient filter on the window, but perhaps that is only effective for IR Cut.

Well, there are people using reflectors that don't have that focus issue.  They wouldn't want to lose those valuable photons 

So it's (IMO) reasonable if the camera window has the widest range.

[Stelios]

Are you sure these aren't blue stars with the center pixels saturated? Is the same thing observed on fainter stars?

[Poynting]

Are you sure these aren't blue stars with the center pixels saturated? Is the same thing observed on fainter stars?

They seem to be blue stars, but in general the blue channel stars appear to be significantly larger than in the other channels, not just for brighter stars:

 

 

The above is from a 12x300" stack.

 

So in this I do see some stars that do not bloat in the blue channel. I guess my question is, should I expect my blue channel to be bloated compared to the others like what is shown? Would an L2 or L3 filter actually help with this? The ASI2600 manual shows that the window has the following bandpass which looks like an L2 filter.

 

Edited by Poynting, 08 April 2021 - 08:45 PM.

[Poynting]

Would you consider this sample to have acceptable CA for a quadruplet (triplet with fpl-53 element, singlet flattener, f/5.8, 100mm)?

 

Perhaps my expectations are too high? Again I have been using a reflector for imaging, but I imagined these "APOs" would be better corrected? I'm ok with being wrong

[cedric_d]

Hi

Same issue with a f/4.4 94EDPH + ASI533MC : https://www.cloudyni...orrection-issue

I'm using an Astronomik L2, ordrered a L3, hope it helps.

[Poynting]

Hi

Same issue with a f/4.4 94EDPH + ASI533MC : https://www.cloudyni...orrection-issue

I'm using an Astronomik L2, ordrered a L3, hope it helps.

Interesting, I will be trying to get an L3 as well. Otherwise I love this scope, seems really well built, and the star shapes and flatness are great. I really want to love it.

[cedric_d]

I started some tests with L2 / L3 and without filters. L3 does not seem to help at all.

More details here : https://www.cloudyni...orrection-issue

[Poynting]

I started some tests with L2 / L3 and without filters. L3 does not seem to help at all.

More details here : https://www.cloudyni...orrection-issue

Thanks for the reply. I just got my L3, and was able to test it last night, but it was very windy and only was able to get a few short subs. So far I think it is helping in my situation, though I will need to test more. I'm sorry to hear it didn't help yours.