Dont be afraid of focal length.

[neil phillips]

Although I believe with the seeing I am getting this winter. I am over doing the focal length. Under better seeing it is possible to shoot at quite high powers with even a 10" scope

Heres a example of a 5x powermate with my SW 300p on the 10th. Not the best by any means. But it gives others a idea of what to look for on there screen. With scopes of 10" and above.

 I may well pull back a bit, as I belive it will tighten the shots. But may also try some 5x shots under good or better seeing, as a comparison.

Don't be afraid to push a little more than you think you can. You might surprise yourself. This is a 3 min capture with the best frames processed. you can see the slight rotation as the best frames alternate between the 3 min capture, put windows on repeat its easier to see

video0001 13-12-10 01-16-27_pipp.avi mmm (3).zip

[Freddie]

What FL does that work out as Neil? I shoot at 9.4m with my CPC.

[neil phillips]

What FL does that work out as Neil? I shoot at 9.4m with my CPC.

Scope is f5. So F25. 1500mm Native FL x5 = 7500 mm.    But that's not the whole picture as the filter wheel is adding more.

What size on screen do your shots look like at 9.4 M Bigger or smaller than this Freddie ?  

[Freddie]

Couldn't open your file, but I'm covering ~3/4 of the height of the DMK21 chip and at 9.4m I'm at F40 which doesn't help.

[neil phillips]

Couldn't open your file, but I'm covering ~3/4 of the height of the DMK21 chip and at 9.4m I'm at F40 which doesn't help.

F Number is misleading it doesn't really tell much to be honest, its focal length that is the info. with my f6.3 Orion and the powermate Jupiter just fits on the chip. With a tiny amount of space above and below. We are really going to far. That's for sure. 6 to 7000mm is likely optimal. we are both above that. The blue shot just posted is that capture size ?

Probably the codec I used. I keep forgetting not everyone has them. I might do another at some point Freddie apologies

[Gartut200]

Couldn't open your file, but I'm covering ~3/4 of the height of the DMK21 chip and at 9.4m I'm at F40 which doesn't help.

Google VLC player. That thing will play everything! Free too!

[Steve Ward]

Can't get your file to work here either sir ... ?

[neil phillips]

Can't get your file to work here either sir ... ?

 I will try another codec soon apologies

[Steve Ward]

No worries sir , look forward to seeing it ... 

[Ibbo!]

I did get it to play

thank you for sharing that

It does show that I need to get my focus much better, how I don't know but I will work on it

Steve

[neil phillips]

OK if you put windows player on repeat, you should get the idea of the capture. As its short. this is high quality uncompressed.

Should open

video0001 13-12-10 01-16-27_pipp.avi vvvvv.avinn.zip

[neil phillips]

I did get it to play

thank you for sharing that

It does show that I need to get my focus much better, how I don't know but I will work on it

Steve

Don't Forget Steve this is the best few hundred frames from a 3 min capture. The  whole capture would not be quite as sharp. But it does show what a high Focal length AVI with reasonable focus looks like.

The way to get these. ( depending on the scope of course ) is to have at least a healthy Focal length. ( 6000mm ) good cooldown collimation focus, and seeing. The rest is good camera control

[Ibbo!]

Thanks Neil

I'm working at 5m so a bit short of your 6m ideal unless I go to the x5 PM but I've only been able to use it a handful of times thats with the 8" SCT

Steve

[neil phillips]

Thanks Neil

I'm working at 5m so a bit short of your 6m ideal unless I go to the x5 PM but I've only been able to use it a handful of times thats with the 8" SCT

Steve

Scope can be the limiting factor. ( apart from good ole blightys weather of course )  You should talk with Angie. She seems to be nailing her work with a 8" sct.

[Ibbo!]

Neil

the corrector plate could do with a wash, collimation is slightly out as well as my focus.

The other factor could be me inside the shed- could even be the main factor

I am thinking of chucking the 300 dob on the large home made mount and trying that, need to sort some motors out first though.

that f13 8" mirror still tempts me though only no tube to put it in as yet.

Steve

[Space Cowboy]

It must be noted that those people using the cmos sensor cams i.e ZWO ASI120 and QHY5L-II need to use aprox 1.5x less focal length due to the smaller pixels and larger image scale these cams produce over the DBK/DFK/DMK/spc900 1/4" sensors. 

[JamesF]

If you work through the maths to find out the point at which the resolution of the camera matches the resolution of the telescope then (surprisingly to me) it turns out that focal ratio is the only variable in town.  Allowing for the fact that pixels are longer across the diagonal than along the edge and that you ideally want to oversample a bit anyhow, I reckon the theoretical maximum useful focal ratio for an AS120 is around f/25 and for an SPC900/DxK21 around f/40.  I don't think increasing the focal length any further gives you any more detail in the image -- you just get the same detail spread over more pixels.

So, as it happens I agree with both Neil and Freddie

I don't believe that's an end to it however.  Seeing undoubtedly plays a part, and some cameras just aren't sensitive enough to produce a useful image in such an extended optical train (or not at a frame rate that is actually worth capturing, at least).

James

[Space Cowboy]

That makes good sense James.

[Freddie]

F Number is misleading it doesn't really tell much to be honest, its focal length that is the info. with my f6.3 Orion and the powermate Jupiter just fits on the chip. With a tiny amount of space above and below. We are really going to far. That's for sure. 6 to 7000mm is likely optimal. we are both above that. The blue shot just posted is that capture size ?

Probably the codec I used. I keep forgetting not everyone has them. I might do another at some point Freddie apologies

The F number does however mean that my scope is quite slow at F40 so my shots are a little darker than would be at a lower F number for a given exposure time. Yep, the blue is just stacked with no drizzle or up/down sizing.

[Stargazer 2013]

Afraid I can't open it to play. I used Avi divx player/gom player/vlc player and quicktime player

[neil phillips]

The F number does however mean that my scope is quite slow at F40 so my shots are a little darker than would be at a lower F number for a given exposure time. Yep, the blue is just stacked with no drizzle or up/down sizing.

Yes of course Freddie, I meant only in relation to a indication of image size scale, FL  A example of this is below. I am apparently at F25 yet

Looking at your blue, when I use the powermate on the 1500mm 300p, it is considerably higher focal length than your blue. How that works out I haven't a clue ?  as you say your at over 9000mm. Yet my 5x 1500mm =7500mm,  Is my filter wheel really adding that much ?

Afraid I can't open it to play. I used Avi divx player/gom player/vlc player and quicktime player

That is odd because the last one is a standard uncompressed avi, that we all use ? Something in the sending to SGL perhaps ? Apologies for that.

[JamesF]

Oh, hang on.  I thought Neil was using an ASI camera, but it looks like you also use a DMK21?  In that case I'd have thought the opportunity is there to go for much more than f/25, though clearly that's going to be tricky with a native f/5 OTA.

Why do you think the filter wheel would make a difference, Neil?

James

[neil phillips]

Oh, hang on.  I thought Neil was using an ASI camera, but it looks like you also use a DMK21?  In that case I'd have thought the opportunity is there to go for much more than f/25, though clearly that's going to be tricky with a native f/5 OTA.

Why do you think the filter wheel would make a difference, Neil?

James

Doesn't the powermate  increase power with increasing Distance James ? Actually I am not sure it behaves like standard barlows ?  F25 seems to be very odd indication here James if you look at the avi it is actually quite a high focal length. Freddie says hes over 9000mm yet my avi looks considerably larger than hes blue. yet hes at F40 ???

[Space Cowboy]

With extension the 5x powermate can reach 7.7x so in theory Neil you could reach f38.5 (11.5m) before it blows your head off.

I know my eyepiece wheel increases fl from f15 to f25 with my 3x tv barlow. Its surprising how extension can up the anti very quickly.

[JamesF]

Ahhh, now, there's a thing.  People talk about the Powermates not working in the same way that barlows do in terms of increasing the multiplier as the separation between the optical surfaces and focal plane.  Powermates supposedly leave this pretty much fixed regardless (give or take 0.5x).  And for the 2x, 2.5x and 4x Powermates that does indeed appear to be the case.

But (I've only just found this out), the 5x powermate is completely different.  It's 5x at the top face of the unit.  Assuming you have your kit set up as focuser->powermate->filter wheel->camera I reckon you could easily have the focal plane 75mm behind the top face of the barlow which would mean it is effectively 7x and all of a sudden you're at f/35 and 11.25m focal length.  There's a fair bit of guesswork about your rig there, I admit.

James