Two questions: DMK41 or get something else? And what about the lunt blocking filter?

[bart1805]

Hello all,
Earlier today I posted the first light of my Bresser Messier 127, F 9,8. I can see there is room for improvement, need more and more hours to get used to everything. But happy with this first light.
A bit unsure about two things.

1. I use a Lunt blocking filter (B1200) with a pst etalon. Would a Coronado Blocking filter be any better? And what would be the effect if I replace the Lunt ITF with a Baader 35NM H-alpha filter? Could be easily mounted. Would it be any better if you look at contrast?

2. The old DMK41. Just 15fps and everything Alexandra says in her beautiful tutorial about it is true. I am thinking about another camera. Not so interested in imaging the whole sun. So normal set up would be with a 2,5 Powermate. Newton rings are no big issue at the moment with the use of a 2 degrees wedge prism. Thinking about the ASI174MM. It is faster, much higher QE, reasonably priced etc. Would that be a good choice or would anybody advise something else?
I think Valery said a couple of times in other topics to use the 174 with f-ratios between 17 en 22. Can somebody (Valery?) please explain why these ratios are the best for the 174?

Thanks in advance for your answers and advice!
Bart.

[Montana]

Hello Bart

I am not good with technical things but 1. Is your Lunt blocking filter performing well? if it is why change it.
2. Yes the DMK41 is great so if you have limited budget and find a good one second hand then that is great. But it is old and slow. If you have the money for the ASI174 then plenty of folks on here get great results but are plagued by newton's rings.

Alexandra

[Merlin66]

If it works, don't touch it....
I have the DMK41 on the SM60/ED80 combo with no Newton Rings. It's a reliable performer.
The ASI 174 I also have is excellent, but definitely needs a T2 tilter up front.
I bought it for the fast frame rates needed for the spectroheliograph, but family and weather have not allowed extensive testing.
(I've also successfully used the Lunt BF on the SM60, no issues no drama.)

[pedro]

I agree with Ken

If it works, don't touch it....

I use CCDs most of the times. PGR (Grasshopper) cameras are great but expensive

ASI174MM (CNMOS) is also a good choice but you will have to deal with noise and newton rings. It's dynamic range is also an issue (considerably lower than CCD cameras)

[robert]

I use a Lunt B1200 with a PST mod. Initially had a Coronado but it rusted and they would not repair it. I have tried replacing the rusted filter in the Coronado BF10 but the Lunt is better anyway. PGR Chameleon 3 is a less expensive 55fps camera (or 36 fps on an USB3 express card as in my laptop), very useful too.
Robert

[bart1805]

Thanks all for your answers! Yes it is true that when it works, don't touch it. But then I would be still looking through my original PST (-;
@Robert: my ITF in the PST was also rusted, I changed it for a filter from Maier Photonics, worked great! Is the pixel size of the PGR Chameleon 3 not to small when imaging at f25? Effective focal length is then 3.000 mm
@Pedro: Problem with the Newton Rings als occurred with my Lunt 60 in combination with the power mate and the DMK41. It also did with the PST mod Skywatcher 100 mm. An the same has happened with the new one. A couple of months ago I bought a 2 degrees wedge prism (part of an ADC). That almost completely solved it for me.
Yep, noise is something I am worried about with the ASI174. But when I am able to image at something between 60- 90 fps, it would be 4 - 6 times faster than the DMK. So there will probably more images to stack in AS!3. Or does it not work that way?
@Merlin: I never tried tilting as someone pointed me to the solution of the wedge prism. Is there any reason to believe that this solution won't work with the ASI?
@Alexandra: The problem is that I find it difficult to compare. I am used to the way the Lunt works and the contrast it provides. But you all have got a point. I will try to find a 2 inch Baader H-Alpha 35 NM filter on the second hand market and just try it out. If it is not any better, then sell it again. And put back the original ITF in the Lunt BF.
Thanks again! Bart.

[Merlin66]

I have another thread where I show the positive effect of the T2 tilter.
The benefit, I think is the ability to vary the tilt angle to find the minimum required to suppress the NR. In my case this was close to 1.6 degree.

[bart1805]

Thanks Merlin, I will read the other thread.