IR DMK41 - Beginner Questions

[Leedsgreen]

Dear All,

I currently use a modified SPC900NC (with b&w Sony ICX098BL ccd) for lunar imaging and have had my eye on the Imaging Resource mono DMK41 (USB) for a good while (mainly due to the vastly increased real estate and 15fps compared to 5fps of the SPC900NC). I have a few questions that I hope some can help with:

1. I know the DMK range have been around for a while now and wonder, in terms of value for money, if anything better has come out since? My main interest is lunar imaging. I have a colour Toucam Pro for the other planets and don’t envisage using a mono cam (with associated filters).

2. Forgetting cost, is anything better than the DMK range? (Although £500 would be my limit).

3. Have Imaging Resource ever indicated that they would be updating their product line?

4. How do DMK mono cams compare to the highly sensitive Sony ICX618ALA ccd (in terms of sensitivity and resolution)?

Thanks very much for any help or advice,

Nick

[brianb]

IMHO the IS DMK41 is still the best value lunar / solar camera out there at the moment. It certainly isn't the best but the price of a Lumenera Skynyx 2.2 is frightening... and I'm not familiar with the larger format cameras in the Point Grey Research range, but software is an issue anyway.

[Leedsgreen]

Thanks Brian,

In terms of resolution and sensitivity, do you know how much difference I will notice over my modified SPC900NC (with Sony ICX098BL)? I have to say, other than fps and chip size, I have been very impressed with it.

Nick

[Merlin66]

Nick,

I have both the DMK21 and the DMK41 for solar imaging and spectroscopy.

They are real industrial strength solid cameras. The ICX098BL chip in the DMK21 is the same as the 900nc with the advantage of long exposure.....the DMK41 has the smaller pixel (4.65micron) ICX205AL chip 1360 x 1024 and again the long exposure option.

I love mine!!

[Leedsgreen]

Merlin,

Thanks for the info. Can I ask, at the same focal length, how does the DMK41 compare to the DMK21 in terms of resolution and sensitivity? Is the only noticeable difference the size of the chip or do the other factors (such as smaller pixels on the DMK41) have an effect?

Finally, as well as my 5" Mak, I also have a SW Equinox 400mm scope. I am correct in assuming the entire moon will (just) fit on the DMK41 chip (or would I need to use a reducer)?

Thanks for any further help,

Nick

[brianb]

how does the DMK41 compare to the DMK21 in terms of resolution and sensitivity?

The sensitivites in terms of photons per square micron are pretty similar. The larger pixels of the DMK21 make it more senitive (shorter exposure at the same focal ratio) but this is almost exactly balanced by the lower resolution ... you need to image at about f/25 with a DMK21 (5.6 micron pixel pitch) to get the same resolution in terms of arc secs per pixel as you get at f/20 with the DMK41 (or DMK31 which also has 4.65 micron pixel pitch.

And of course you get a much bigger area imaged with the 41. This is a big help with lunar & solar surfaces ... for planets, the higher frame rate achieved by the 21 is a big help.

I have a DMK41 and a DMK21 ... and use them both. If you can afford only one, and want to do planetary work as well as lunar and/or solar work, the DMK31 is a good compromise.

[riklaunim]

4. How do DMK mono cams compare to the highly sensitive Sony ICX618ALA ccd (in terms of sensitivity and resolution)?

ICX618 is 2-3x more sensitive than ICX098 and similar CCDs. You can put it in DMK21 or a Webcam. Cameras designed with ICX618 such as Basler Ace, PGR Flea 3 or QHY IMH0 costs much more (Basler about 500-550 EUR, QHY cheaper as it's USB).

For lunar/solar ICX445 is getting much attention. 1/3" with small pixels and quite high sensitivity. Found in fast Basler and PRG Flea 3 (GigE camera and Firewire 800 camera).

[Leedsgreen]

Thanks all for your very useful replies,

If I've read correctly:

1. There are more light sensitive CCDs on the market compared to the ICX205AL (DMK41), however, these usually cost much more (say four times as much)?

2. Whilst the ICX098BL chip in the DMK21 has larger photosites than the DMK41, in terms of image resolution there is less difference in light sensitivity (i.e. DMK21 would have to work at f/25 to match f/20 in DMK41).

All things considered, it appears the DMK41 might best suit my needs. A few more q's (if OK):

1. Is the best price still around £475?

2. Would the DMK41 be able to fit entire moon on chip with 400mm refractor or would I need to use 0.8x focal reducer (for example)?

3. Is the supplied software as easy to use and intuitive as, say, Astrocapture that I currently use for my SPC900NC? Could I use Astrocapture with the DMK range?

4. Will I always get 15fps from DMK41 or does this depend on a host of factors (i.e. such as shutter speed and other settings)?

Thanks again for any help, it's much appreciated,

Nick

[brianb]

1. Apparently so.

2. The lunar (or solar) disc fits reliably and comfortably on the DMK41 with 400mm focal length. The DMK31 chip is just a bit too small. At 480mm focal length, so is the DMK41.

3. I find IC Capture very easy to use ... sorry but I don't know Astrocapture.

4. 15 fps is the maximum speed you will get with the DMK41. It can be configured to run slower (in powers of two, i.e. 7.5 fps, 3.75 fps ...) and will run slower than the frame rate set if the shutter speed is longer than the interval between frames.

[riklaunim]

And note that D*K cameras are affected by circular artifacts, which usually show on planet images. The bug is for max speed so with DMK41 you won't be able to use 15FPS, but only 7,5FPS to avoid them. This would be very slow for planetary imaging...

And it's very hard to buy good planetary and good lunar camera in one - unless it has ROI and ROI size dependent speed. This is done AFAIK for Lumeneras as well in Basler and PGR.

[brianb]

note that D*K cameras are affected by circular artifacts, which usually show on planet images.

I've found this happens very rarely. Full speed imaging is fine for solar surfaces, I've never had an issue.

[riklaunim]

I have that nearly any time on Jupiter if DMK21 goes to 60FPS. On the other hand at f/20-28 sensitivity doesn't allow going faster than 30FPS.

[Leedsgreen]

Thanks once again everyone for replies,

My sense is that there are always compromises to be met when making a choice (unless one is prepared to pay £000s)! Not wanting to start a debate, I wonder if the DMK31 would be a good compromise (as first suggested by Brian). What I mean is, it is larger than the DMK21 and hopefully it could run at 15 fps without any of the artifacts that Riklaunim mentions?

All this talk has made me think of another question (which I hope is OK): It appears that the ICX618 is 2-3x more sensitive than ICX098. Does this mean that as the ICX618 can work at a higher shutter speed, there will be substantially more clear frames to stack for a given run? Whilst the DMK41/31 is appealing for size, part of me is now considering buying a DMK21 and having the ICX618 fitted. My question is, would I notice the difference in quality for lunar imaging comapred to the ICX098 or ICX205AL (I know I would for other planets)?

Thanks again,

Nick

[beamish]

Nick, It's worth remembering what has been said already i think, you can change the chip but you'd still be limited by the firmware/ software to fps etc, also buying an ICX618 chip and putting it into a host means you'll probably end up spending far more than simply buying a PG Flea 3 or B ace straight off. The qhy cam seems to be taking an age to hit the wider market and is not cheap. I don't know what capture s/ware Rik uses for his Ace but the PG flea 3 will work with Firecapture and hopefully with Lucamrecorder by next year. The PGF3 costs 695.00 USD ( don'tknow what the shipping costs would be) =433 quid -Not bad !

[riklaunim]

DMK21 electronics allow 60 FPS max, but it gives artifacts. Even if you change the CCD the problem will still be there. Sensitivity will allow to shoot ~60FPS at around f/20, but the artefacts can/will show up. Emil did the DMK21 with ICX618 mod and it did not removed the artifacts.

IMHO:

- find second hand DSI III Pro in USA - can do solar/lunar/ds and in some excent - planetary (but low speed 16 bit requres excellent seeing)

- then if you want to go more advanced for planetary hunt for Lumenera second hand or QHY5v/QHY5 as a cheap DMK21-like camera (and a guider). Very advanced - the expensive new cams Or maybe wait for QHY IMG0H. Some initial pricing was bit above DMK21.

[beamish]

I think there's still a Lumenera 070m for sale on AB&S