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Mallincam and bloated or blown out stars

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#1 chuckscap

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Posted 04 May 2013 - 01:07 PM

Hi, almost all of the Mallincam images I've seen have bloated or blown out stars. Are the bloated stars due to the fact that folks are using alt/az scopes and have too long exposure times or EQ mounts with bad polar alignment? The blown out stars are more concerning, does the Mallincam not have averaging software (mean or median) just accumulation or is once again new folks just starting out. Not trying to diss the camera or the folks using it, considering buying one, but want to know what's what.

#2 mclewis1

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Posted 04 May 2013 - 03:05 PM

Chuck,

There's a variety of reasons why you'll see stars like that with Mallincam or other video cameras.

The vast majority of folks using video gear are looking for as fast an image display as possible so very high gain is often used. This allows the faint fuzzies to be displayed in only a matter of seconds but does over do the stars a bit.

High gain with video is also often coupled with extra sharpness and this can lead to dark halos around brighter stars ... the "owl effect" some call it.

In the quest for speed very fast optics are often used. In some cases this means aggressive focal reduction which is often at the expense of some optical quality, so the stars are sometimes a little larger than necessary.

If someone wanted smoother images (rather than the fastest possible reproduction) from a video camera all they would have to do is adjust down the gain and sharpness and possibly dial back the focal reduction (this depends on the focal reducer used and how aggressively it's setup). You can produce very nice smooth "CCD like" images with a Mallincam Xtreme camera by using what is called CCD mode.

If you are curious about better images specifically from a Mallincam I would suggest joining the Yahoo Mallincam group and have a look at Chris Applegate's (postings and NSN broadcasting also under the name of Astrogate) images taken in CCD mode (he has quite a selection of images posted, you'll need to look specifically for the ones taken with CCD mode). There are also a few other folks on the group who have posted really nice images using CCD mode.

Overall using CCD mode isn't that popular, most folks want speed above all else but it does show what a Mallincam Xtreme video camera is capable of.

#3 Spacetravelerx

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Posted 04 May 2013 - 03:36 PM

Mark, I never thought of CCD mode. I need to try that out!

I am still learning and playing with this thing. I love it though!

#4 chuckscap

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Posted 04 May 2013 - 04:31 PM

Thank you Mark, that really helps. I've only done a bit of imaging with my original Canon Rebel, and I know it can be difficult to get nice round not blown out stars and still bring out the fainter stuff. I'm just getting into video astronomy so I went cheap and just purchased a NexImage 5 with a .5x focal reducer (total a whopping $224!). I plan to run DeepSkyStacker Live and see how things go.

Thanks again!

#5 Dwight J

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Posted 04 May 2013 - 08:36 PM

Hi Chuck: you didn't say what type of scope you use. A refractor can benefit from an infared filter although this is at the expense of some sensitivity. Such a filter can also shrink stars in other scopes that have some glass like SCT's. Adjusting APC can also make stars smaller but this can cause black rings around stars if used too aggressively.

#6 chuckscap

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Posted 05 May 2013 - 12:07 AM

You're going to laugh because I'm mostly a visual observer and I have pretty high end equipment compared to the camera I bought. I have a Mewlon 250 with in baffle corrector. I got it pretty cheap since it had a small dent in the OTA but the optics are perfect. It sits on a vintage Parallax HD 150 mount I also got really cheap but had to put some money into.

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#7 mpgxsvcd

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Posted 05 May 2013 - 11:35 AM

Simply put it is due to dynamic range. In order to see very dark objects surrounded by very bright objects you have to have a lot of dynamic range. Much more than any sensor can capture in the case of the darkest objects.

The less dynamic range you have the more the stars will clip or blow out.

You can simulate more dynamic range through HDR images. However, the final image still has the same dynamic range it is just that you are compressing the dynamic range of the scene you are capturing.

You can also block out some of the light from the stars with very strong filters. Although you also have to make sure that you don't take out the light from the object you are looking at as well as the light from the star.

#8 GlennLeDrew

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Posted 06 May 2013 - 11:18 AM

Fundamentally, it comes down to pixel count. A ~300,000 pixel CCD does not have the same fineness of image as that of an 8,000,000 pixel CCD. It's completely unfair to compare images captured with devices of such fundamental divergence.

If one wishes to compare devices, crop from the bigger-CCD image a same-size array as that of the smaller CCD, and display to the same scale. Now you will be examining relevant differences.

And on top of the low resolution (as a function of image width), analog video suffers the smearing of chroma bleed, among other not-so-garish artifacts.

#9 chuckscap

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Posted 08 May 2013 - 08:20 PM

Thanks Glenn, I hadn't thought about the "digital zoom" effect of using far fewer pixels. I ordered a NexIMage 5 and have downloaded DeepSkyStacker Live. I'm anxious to see what result I'll get using them on DSOs if the skies ever clear here in sunny Colorado

#10 rmollise

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Posted 09 May 2013 - 06:56 AM

Thanks Glenn, I hadn't thought about the "digital zoom" effect of using far fewer pixels. I ordered a NexIMage 5 and have downloaded DeepSkyStacker Live. I'm anxious to see what result I'll get using them on DSOs if the skies ever clear here in sunny Colorado


I can tell you the results... If you can get the NexImage down to a fast focal ratio, f/3 or f/4, you can capturebrighter objects pretty well. I used one to get Comet Holmes some time back. But it will not be an Xtreme. ;)

#11 chuckscap

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Posted 11 May 2013 - 04:46 PM

Thanks Rod






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