ASI120 mono or Dmk 31

[Astroblagger]

Hello I want to upgrade my dmk 21 FireWire camera been looking at the dmk 31 or ASI120 which would be better??

[james_screech]

I haven't used a DMK31 but have a DFK31 and a ASI120MM. Looking at the specs the ASI120MM has a better peak sensitivity, and has higher resolution. The ASI120MM gives much better images IMHO and supports ROI, so it can support much higher frame rates. The ZWO (makers of ASI120MM) LRGB filters and filter wheel are reasonable as well.

James

[stoffe]

ASI120MM all days in the week! My astro club has a DFK31 and I got a ASI120MM camera, many TIS cameras have problems with higher framerates (30 fps and over) and often got union rings after a final stack or other faults, I do not know why. And there is two other aspects too.

TIS cameras are not made for astromomy, they are industrial cameras.

ZWO cameras are special developed for astronomy use and works very well, you need a fast computer for this one! But it works very well on a Core2Quad computer, and also on Core2Duos. But early Core2Duos and Pentium 4 might be too slow. Get 4 GB RAM as well, it cheap nowdays.

[james_screech]

One technique I use to improve the frame rate is to use a RAM disk to save images too. Even the disk on my 2.6GHz dual core laptop cannot keep up with the ASI120MM, so I use 3GB (out of 6GB) as a RAM disk and save images there, then after each capture copy them to the hard disk.

James

[allcart]

I use a DMK 31 and 41 mono versions and have never had onion rings (newton rings) on my images although I'm sure i have seen posts about that propblem with the ZWO120. I haven't used a ZWO120 so cannot verify this.

I don't think you can rule out a TIS cam just because it is an industrial camera. Point Grey also make industrial cams but are fantastic cameras for solar imaging.

A lot of astro cameras started out life as something else and have been modified for astro use. Likewise a lot of great video astronomy and planetary cameras started out as cctv cameras and web cams.

[stoffe]

My experiences with TIS is only with the Firewire cameras and the DMK21 (I got one here) have the newton ring problem, especially on higher frame rate  and I have never seen a ASI120 camera with that problem. The problem is more often that the ZWO cameras require a really fast USB port to work as expected.

I think Point Gray Flea cameras is better then TIS, they have a USB3.0 interface too, there are also more alternatives like Baasler Ace and so on. Here is a comparison list between lot of different planetary cameras.

http://nicolas.dupontbloch.free.fr/camera.htm

[Ibbo!]

depends what you are wanting to use it for.

I have both

I like the ZWO for planetary but on solar Ha it is a nightmare for Newtons rings

Steve

[IanWatkins]

Never seen Newton rings while imaging (solar) on the DMK41 i had either. Was just never a problem nor was capturing at high frame rates on a crusty old netbook running a 1.6GHz Atom processor with 1GB RAM and a 5200rpm hard disk. Would capture all day without issue (other than disk space). OK, that was uncompressed video but worked just fine.

Going back to the original poster, what is it you want to image? This might get you some better advice.

Cheers

Ian

[michael.h.f.wilkinson]

I gather the CMOS chips used by ZWO are more prone to Newton rings (my ASI130MM certainly does) than the CCD chips used by DMK cameras. Newton rings should also not depend on frame-rate, so I wonder if the phenomenon described is not a case of onion-ringing due to inadvertent use of low dynamic range of the ADC due to short exposures.

[allcart]

Thanks for the interesting link Stoffe

[Zakalwe]

Hmmm...it depends on what you want to do. I've seen a few problems with ZWO cameras when imaging bright objects (Solar and lunar), with Newton rings. I think that there might be issues with the rolling shutter creating artefacts.

For planetary, the ZWO is getting tremendous results.

So you need to factor in your preferred choice of target & your scope (small pixels best for f20~).

The DMK range is getting a bit long in the tooth now, though they are still great cameras. There are better as well as cheaper options out there now.

[james_screech]

With my DFK31 I get onion rings on planets about 80% of the time, with the ASI120MM 0%. I haven't tried either to solar and only a DFK31 a few times for lunar so cannot compare them on those targets.

I have seen some impressive deep sky images taken with the ASI120MM especially when you consider it only has a 12bit ADC (DxK are only 8bit).

James

[Zakalwe]

With my DFK31 I get onion rings on planets about 80% of the time, with the ASI120MM 0%. I haven't tried either to solar and only a DFK31 a few times for lunar so cannot compare them on those targets.

Onion rings are caused by having the gain too low, or the chip not being sensitive enough. The ZWO is a heck of a lot more sensitive than the older DMKs, hence why it's doing so well with planetary imaging.

Again, it comes back to being clear on what the camera is required for and the scope that it is going to be used on.

[Astroblagger]

I do lunar/solar(Ha)/ and planetary. I've just seen quite afew solar shots with lines and rings?

[stoffe]

If you get lines with the solar h-alpha imaging with a ASI120MM you need to take solar flats. Here is a very good guide of how I got rid with my lines with a Lunt 60 h-alpha telescope.

http://www.schursastrophotography.com/solar/Articles/solararticle5.html