Dont be afraid of focal length.

[JamesF]

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

Eh?  I know there's a 3x TV barlow (I have one .  I didn't know there was a 3x Powermate.  Is that a typo, or am I missing something?

James

[JamesF]

There's a handy graph on this page, Neil: http://www.televue.com/engine/TV3b_page.asp?id=53&Tab=_app

James

[neil phillips]

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

Theres the explanation  Right there James ( Cheers Stuart completely correct ) I am likely at about 11 meters ish John H Knows a formula to calculate it from measuring the planet. But 11 meters ish is accurate enough for me

[Space Cowboy]

Oops! Sorry I meant 3x tv barlow.

[neil phillips]

Cheers for the graph James. I remember that one

[neil phillips]

Oops! Sorry I meant 3x tv barlow.

Lol easy done

[Freddie]

Hi Neil, just looked at that B I posted and I must have done a crop while converting to JPEG so it is not an accurate size (in relation to the border). I also use a powermate and my understanding is that unlike a barlow the FW would not add to FL. In theory I am therefore slightly larger than you on capture due to the extra ~1m FL.

[neil phillips]

Hi Neil, just looked at that B I posted and I must have done a crop while converting to JPEG so it is not an accurate size. I also use a powermate and my understanding is that unlike a barlow the FW would not add to FL. In theory I am therefore slightly larger than you on capture due to the extra ~1m FL.

The 5x is different Freddie. apparently it does add power with extension. I am considerably over 9 meters

[Space Cowboy]

Ok, ok enough of the boasting!  

[neil phillips]

Ok, ok enough of the boasting!  

LOL scale wars

[neil phillips]

Was pretty confused by the comparison with Freddies blue though. If it was cropped that helps explain whats going on. As does the filter wheel extension making the setup more than F25

[neil phillips]

Ok, ok enough of the boasting!  

Over 9 meters of blur and trouble for the most part actually lately

[SnakeyJ]

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

Nice instructive thread and some very useful posts as well.   I failed to get either video to play on my android phone unsurprisingly, but works a treat on my office computer. 

Interesting point from JamesF on the TV PM x5 - I had also assumed that this was a telecentric extender and was not affected by extension!

Working with my Revelation x5 ED barlow before the filterwheel I can achieve focal lengths of around 6600mm or F33 with the Explorer 200P - though I've yet to achieve anything useful at this extension!     However, the QHY5L-IIM is sensitive enough to respectable 50-60FPS on Jupiter with a 640x480 ROI on Jupiter at this f/l even if the resolution @ 0.12"/pixel is well beyond the capability of the scope and excellent seeing!

[Space Cowboy]

Mars in the spring should handle the big stuff though not as well as 2 yrs ago when it was higher.

[neil phillips]

Mars in the spring should handle the big stuff though not as well as 2 yrs ago when it was higher.

That is where it becomes useful agreed Stuart. Time to practice spring has better seeing here. So maybe worth some time with Mars

[cgarry]

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.

Neil,

I noticed you tried to produce videos using the ULRG codec and the DIB codec.

I have updated the FMP4 codec (lossy compression) in PIPP (v2.2.21) to allow for a higher quality videos to be generated.  The new quality level 6 is the same as the old quality level 10 and the new quality level 10 has a 2.5x higher bitrate than the old quality level 10.  Put simply you should be able to generate better quality compressed videos!

Cheers,

Chris

[neil phillips]

Nice instructive thread and some very useful posts as well.   I failed to get either video to play on my android phone unsurprisingly, but works a treat on my office computer. 

Interesting point from JamesF on the TV PM x5 - I had also assumed that this was a telecentric extender and was not affected by extension!

Working with my Revelation x5 ED barlow before the filterwheel I can achieve focal lengths of around 6600mm or F33 with the Explorer 200P - though I've yet to achieve anything useful at this extension!     However, the QHY5L-IIM is sensitive enough to respectable 50-60FPS on Jupiter with a 640x480 ROI on Jupiter at this f/l even if the resolution @ 0.12"/pixel is well beyond the capability of the scope and excellent seeing!

I really need to get this new chip don't I Jake. I think the extra sensitivity will help what I am trying to do. Everyone cant be wrong

[neil phillips]

Neil,

I noticed you tried to produce videos using the ULRG codec and the DIB codec.

I have updated the FMP4 codec (lossy compression) in PIPP (v2.2.21) to allow for a higher quality videos to be generated.  The new quality level 6 is the same as the old quality level 10 and the new quality level 10 has a 2.5x higher bitrate than the old quality level 10.  Put simply you should be able to generate better quality compressed videos!

Cheers,

Chris

Cheers Chris I tried earlier but for some reason it wouldn't process I will have to go back and check what it said on Pipp. Something I am likely doing wrong.

[JamesF]

John H Knows a formula to calculate it from measuring the planet. But 11 meters ish is accurate enough for me

We're not that far from opposition, so Jupiter is going to be about 50 arcseconds wide at the moment.  From memory the DMK21 has 5.6um pixels, or 0.0056mm, so the focal length in mm is given by:

fl = 206265 x 0.0056 x ( diameter of planetary image in pixels ) / 50

A quick check against the images I get from my 127 Mak an ASI120 suggest that looks right.

James

[JamesF]

Oops! Sorry I meant 3x tv barlow.

Jolly good.  For a moment there I thought I'd perhaps missed a new product

James

[SnakeyJ]

I really need to get this new chip don't I Jake. I think the extra sensitivity will help what I am trying to do. Everyone cant be wrong

I think the ZWO ASI120MM is probably better from a driver and support perspective, though it is a little more expensive.    That being said, the only issues I've had have been with LX, rather than high frame rate PI.      The QHY5L-II's 1.25" form is also really nice in giving some freedom to vary focal length and its a lot lighter as well.

Might be worth checking out the newer e2v ruby sensors might be worth a look as well - I think IDS and Basler do some USB3 industrial cameras based on this which are supported in Firecapture.     

[JamesF]

We're not that far from opposition, so Jupiter is going to be about 50 arcseconds wide at the moment.  From memory the DMK21 has 5.6um pixels, or 0.0056mm, so the focal length in mm is given by:

fl = 206265 x 0.0056 x ( diameter of planetary image in pixels ) / 50

By way of explanation there, the generalise form would be:

focal length = 206265 x ( pixel size in mm ) x ( diameter of planetary image in pixels ) / ( apparent size of planet in the sky in arcseconds )

thus you can work it out for any planet at any time with any camera.

The 206265 is a "magic" number that falls out of the trigonometry.  It's actually the number of arcseconds in one radian.

James

[JamesF]

I think the ZWO ASI120MM is probably better from a driver and support perspective, though it is a little more expensive.    That being said, the only issues I've had have been with LX, rather than high frame rate PI.      The QHY5L-II's 1.25" form is also really nice in giving some freedom to vary focal length and its a lot lighter as well.

Having both the ASI120 and QHY5L-II (mono) I was pondering on this the other day.  The design of the QHY does make for easy tweaking of the focal length and I like that the USB socket is on the back rather than the side, but cleaning the sensor is a bit awkward and I like the case design of the ASI from a temperature control point of view.

James

[Space Cowboy]

I've been getting a lot of noise with my QHY James and I wonder if its down to the small size creating heat especially at the fastest frames rates. Would be very interesting to do a side by side comparison of the ZWO and QHY cams.

Having said that Damian Peach produced a killer Jupiter shot the other day with the QHY.

[cgarry]

Cheers Chris I tried earlier but for some reason it wouldn't process I will have to go back and check what it said on Pipp. Something I am likely doing wrong.

Since I have been changing stuff in this area it is always possible I have broken something!  Please do let me know if you do see any issues and I will get them fixed.