The attached was recorded Tuesday 7 Oct around 7 -15 pm, 700 frames at 60 fps and stacked in Registax. The original image isn't in perfect focus and it has been sharpened with Unsharp mask to enphasize the problem for presentation. Every capture taken are distorted with these ridges. Can some member provide an answer.
Thanks Mike. I did use an extension cable to the DMK for the first time and I had a 240 volt AC flex to the Computer both could have been close. I would have thought USB cables to be shielded, but I'll try not to use the extension and keep AC well away. I checked the collimation and found it wasn't spot on, but very close and thought it could be the problem. I submitted a question yesterday regarding the star check which I wasn't aware of until reading Al Sheelan's reply to collimation. I'd appreciate a reply to this. The codex is Y800 The first clear good viewing in two months and I failed. Very disappointing! The strange thing is I got a reasonable shot of Jupiter which was close to the moon and captured the two Jupiter's moons with the planet. I'll attach it for comment.
Mike. The attached captured last night at 7 pm , again 700 frames . No extension USB cable and the 240 v flex kept well away from the scope. Conditions wasn't as steady, but I think you will agree there is an apparent difference. I'm still having difficulty in detecting perfect focus. I use a long 2x Barlow with the DMK. The focuser focuses the image reflected from the primary and secondary onto the Barlow lens. What I cannot understand is the distance from the lens of the Barlow to the face of the chip in the DMK, is a predetermend set distance. I would have thought the distance from the Barlow lens to the chip face to be very critial. The letters r p c represent a code I use . R= Registax P = Photoshop and C= colour added.
Any comments?
That last lunar shot looks much better, Dennis! Looks like the USB cable isn't shielded. I have a USB extension cable that I know is shielded - it has a steel braid around the outside, but generally I'd be surprised if they are shielded.
Focus is often difficult... the worse the seeing is the harder it is to focus IMHO. I have tried the Hartmann mask, and the K3ccdtools focus aid, but in the end I think I've had best results by careful adjustment and taking a bit of time to watch the frames being captured... if I'm getting brief flashes of sharp frames through the seeing, then I know there's no point tryin to focus sharper. Then I use registax to select the sharp ones... sometimes you don't end up with too many to stack, but even 30 is considered the lower end of statistical validity.
I get a LOT of noise like you have in the first moon shot when I use a frame rate too high for my camera / conditions (like 60fps), it looks almost like a vertical hold problem on old CRT TVs.
The second one looks great, so perhaps its a combination of running the camera FPS too fast and the noise from the USB cable also.
Thanks to the thread and to Al for bringing this to my attention, I will try it with mine and see if I can reduce the crap noise I am getting..
I'm interested to know if you can focus on a star (with a Hartmann Mask) then swing to the moon and have it in focus? This is how I've been setting up for Jupiter. I realise they are going to be different distances away but is that going to make a big difference to the focus point?
I'm interested to know if you can focus on a star (with a Hartmann Mask) then swing to the moon and have it in focus? This is how I've been setting up for Jupiter. I realise they are going to be different distances away but is that going to make a big difference to the focus point?
Peter
Yep! That's the way to do it. The moon is just as much at infinity as the stars for all practical purposes.
Thanks Al and Chris, your comments regarding focus are much appreciated. I made a Hartmann mask and gave it away and returned to visual focus. The two speed remote focus works perfectly, but atmospherics and age still makes it difficult to get that exact point. It's a guess most times but occasionally one gets it spot on. Thanks Bassnut for your comments, but I'm confused with the suggestion over stretched. Is this term associated with FPS? I must admit I mostly use 60 fps. How does one decide when to use 30 or 60 fps?
I'm still concerned with the focus of the Barlow onto the DMK CC chip. I fail to understand how the Toucam I had and the DMK I'm now using, can both be in focus when both are a different length from the face of the chip to the Barlow lens.
When I recorded Jupiter and the two moons, something I've only achieved with the planet being over exposed, it came as a surprise. The following evening I tried again but no moons just a shadow on the planet.
I'm using a 250 mm GSO on a Eq platform DMK 21 and 2 x Barlow. Registax and Photoshop 5. One dissapointment is the difference between the laptop display and the desk commputer that sends these pictures. What looks great on the laptop is dark on the desk computer.
Wow, those moon shots you just posted are great! focus looks spot on to me, nice and sharp.
With respect to the FPS, 30fps and 60fps is probably too fast on bright objects, there will be alot of noise in the image, Mike Salway may be able to recommend what speed you should use for the moon and Jupiter with a DMK, I know my Toucam doesnt like anything over about 15fps on Jupiter, it gets very noisy and stripy like you saw in the first moon shots.
I must admit I mostly use 60 fps. How does one decide when to use 30 or 60 fps?
Hi Dennis,
Really nice Moon, shots focus looks spot on.
To determine what frame rate you should use. I usually have a look at the histogram and the brightness of the object. Say if you are imaging the Moon, because it is so bright you can easily use 60 FPS. But say for example, you are imaging Saturn, which is not all that bright. It is better to use a slower frame rate around 30FPS or even 15FPS to properly expose the object.
All you have to remember to do is correctly expose the histogram.
By "stretched" I mean increasing the dynamic range in PS with curves (or whatever prog you use) untill the brightest parts saturate. This then can also bring up artifacts, and you lose detail in the saturated areas. The 2nd pic post look much better tho, very sharp and detailed indeed. As Matt says, always watch the histogram and avoid clipping at either end (saturation will show as a clipped histogram).
Matty P and Bassnut.The histogram stumps me. After reading your comments, I've read most of all that is provided by Google on the subject and am no nearer understanding how I can set my exposure on the DMK 21 with the histogram that doesn't appear to be provided. There is one on Registax which provides adjustment and another on Photoshop which doesn't appear to be adjustable. After reading the information provided by Google I can only assume you both use a CCD CAMERA which displays a histogram for exposure setting?
Can you advise a source of available information? Or advice on exposure. I set Gamma at around 100 and leave it. Set the gain sider fully to the left and set the exposure to enable the subject to be seen, a little on the dark side to avoid over exposure.
I'll be giving FPS thought from your comments which are much appreciated.
If you use a progam like K3ccdtools or WXAstrocapture they have built in histograms that show you the exposure levels real time and allows you to avoid overexposure during capture. Try these with the DMK and you will see what we mean, they are both free.
. I have a USB extension cable that I know is shielded - it has a steel braid around the outside
, but generally I'd be surprised if they are shielded.
Then I use registax to select the sharp ones... sometimes you don't end up with too many to stack, but even 30 is considered the lower end of statistical validity
.
