DMK,, firewire or USB

[Lester]

Hi all,

I have not seen the necessity to go to a mono camera, until I experienced the good seeing that I have had in the last month.

I am thinking of the DMK type camera, but can someone inform me on the advantages and disadvantages of the Firewire and USB types?

I already have a powered hub that I use on the DFK camera.

Thanks.

[matt]

Hi Lester...

With the USB version, you won't need to use your hub. You also won't need as many cables, which has its obvious benefits in the field.

[Lester]

Thanks for your reply Matt.

That is 1 big advantage for USB.

[iceman]

Hi Lester

I love the USB version. Not having to have the powered hub and the PCMCIA firewire card were 2 great advantages.

My newer USB one can also do 60fps to the external hard drive easily, but I had problems with 30fps using the firewire version.

On a window box, I reckon USB is the way to go. It's got plenty of bandwidth for the data transfer you'll use.

[Dennis]

Hi Lester

Cameras capture a lot of data that needs to be sent to your computer hard disk, quickly. Firewire and USB are high speed data buses designed to manage these large volumes of video (and audio) data.

I think that The Imaging Source Firewire camera are Firewire version IEEE 1394a, designed to transfer data at 400 MB per second, and The Imaging Source USB camera are USB2, designed to transfer data at 480 MB per second.

I also understand that as there is some overhead in how each implementation works; the actual speeds are always less that 400 and 480 MB/s respectively. Allegedly, in the real world, it appears that Firewire (at 400MB/s) actually has a greater throughput that USB2 (at 480MB/s).

I have also read that there is a Firewire version IEEE 1394b at 800MB/s and a new USB3 which is to be released soon.

However, in practical terms, it seems the bottleneck on our laptop computers tends to be the speed at which the data can be written to our hard disks. Desktops Hard disk drives tend to operate at 7200rpm whereas laptop HDD’s tend to run at 5400rpm, some older models even at 4000rpm.

So, I suspect that if you have a modern laptop, in terms of speed, Firewire or USB will be okay, it just depends on ease of connectivity and getting sufficient power to the camera.

I have a Firewire DMK and have to use a powered PCMCIA card to connect it to, which is not as elegant a just plugging a USB camera into a USB2 port on your computer.

Cheers

Dennis

[Lester]

Thanks for your replies.

What is a PCMCIA card? I only use a powered hub for the DFK and have had trouble sometimes getting 30fps.

My laptop was new early last year and was the top of the range Toshiba then. Its a A300.

[Dennis]

Hi Lester

Older laptops had a slot in the side for a PCMCIA card, which is a thin card that plugs into the laptop to extend its functionality by adding e.g. Firewire, extra USB ports, Bluetooth, etc. I think it was later known as a PC Card?

Newer laptops have something called an “Express card” and they are not interchangeable. That is, an old PCMCIA card will not plug into an Express Card slot and vice versa.

Cheers

Dennis

[Paul Haese]

Lester as said USB2 is fine. The bottle neck problem will the least of your problems in all this. Reason being that you will not have enough light even with a 14" scope to attain values greater than 40-45 fps. In practice you will fine that around 35 fps will fully illuminated the histogram in each channel, much beyond that and you must trade off speed for illumination.

This becomes more evident once you use more magnification. The most I can get with my C14 at around 14,000mm of focal length will only allow 30fps at the very most. That is with gain nearly at full and exposure at around half way. Remember that is with a skynyx which is more sensitive than the Imaging source camera's

So in real terms you are likely to image at around 12,000mm or so and expect to get something like 30fps with a hard drive that can take that much data at once. From memory you have 4gig of memory and this will help in the data transfer equation. Therefore a USB DMK will be fine.

[Lester]

Thanks again Dennis.

Looks like it will be the USB type for me.

[Lester]

Thanks for your input Paul, I appreciate it.

[Lester]

Hi again, been doing some homework on the species of these cameras.

The DMK21au04.AS has a unit cell size of 5.6u.m x 5.6u.m and 480TV-lines.

The DMK31au03.AS has a unit cell size of 4.65u.m x 4.65u.m and 768TV-lines.

Does that equate to the DMK31au03.AS having better resolution of fine detail?

Thanks.

[iceman]

Hi Lester,

The DMK31* has a bigger chip so you get 1024x768 resolution, but a smaller pixel size (4.65um) - what that means in practise is a bigger image, but less well depth and less potential dynamic range - therefore less sensitivity.

For planetary imaging, the DMK21* is better than the DMK31 or 41 series.

Check out my reviews for comparisons of the 31 and 41's versus the 21.

Review of the Astrovid Voyager X (http://www.iceinspace.com.au/93-447-0-0-1-0.html) (has the same chip as the DMK31)

Review of the DMK41AF02 (http://www.iceinspace.com.au/93-527-0-0-1-0.html) (and comparison vs the DMK21).

[Lester]

Thanks for answering my question Mike.

I know that in the past the 640x480 chip when imaging Jupiter near opposition that the planet is almost over the edge of the screen. So I thought a slightly larger chip would be benificial, but not at the expense of less sensitivity.

[iceman]

Too right - I know what you mean about the 480px height, but it's worth scaling back the focal length in those instances rather than sacrifice sensitivity.

[Merlin66]

My 2c
I've been using the DMK21, firewire on an Acer laptop for the last year or so.
Bought the powered firewire cable which allows connection to the smaller 4 pin firewire socket on the laptop and a 12V power supply. I use a 20Ah gel cell battery, which seems to last forever.
Imaging on the SolarMax 60 Ha scope I use exposures from 1/2000 sec to 1/8 sec. This is independent of the frame rate; with exposures less than 3.5sec the exposure takes precedence over the frame rate.
A great camera!!!

[Paul Haese]

Lester, you will find that using a 2x and a filter wheel will produce a very large image scale on the screen. At last years opposition I had around 15-20 pixels each side of the planet in the 480 height. Given that this years opposition Jupiter will be around 49 arc seconds and then the next 2 will be 50" using anything above a 2x barlow will be not viable.

[Lester]

Thanks for that info Paul.

I have just got home from Adelaide and got myself the firewire DMK; because the supplier had them at a good price, as he got them when our dollar was on a high last year. The price was $390 and the DMK with current exchange would be $200 more.

[iceman]

Good to hear it, Lester. The firewire will be fine if you're used to working with the hub etc.

When are you going to get the filter wheel + filters?

[Lester]

Hi Mike,

I have just found that the firewire type cameras are not compatable with PHD tracking. Matthew Lovell is looking into it for me. I didn't even think of this problem. I noticed on the Imaging Source email that there was a new tracking program, but couldn't open it to find any such information.

I got some Baader Planetarium filters and a Atik manual wheel. I will not use this camera until I get an answer to this problem. Even if it means getting a USB DMK for $200 more, just so I can use it for imaging and tracking.

Just to add to all that, I have now got a Losmandy Titan sitting here waiting to get fitted to the pier. I am a bit tempted to leave the Titan till Jupiter passes opposition, or we get a week of cloud.

[Merlin66]

Lester,
I have the DMK21 firewire, use the "Firewire Performance Manager" a free download from Imaging source. I'll set it up later this morning with PHD and see what happens!
I usually use the QHY5 for guiding; hadn't heard of this issue with the DMK.... keep you posted.

[Lester]

Thanks for doing that Merlin, this is all new to me, so much appreciated.

[Dennis]

Hi Lester

The PHD website at Starklabs (http://www.stark-labs.com/phdguiding.html)indicates that PHDGuiding works with The Imaging Source (Windows and OS X) Cameras?

Is the issue then whether it works only with the USB model, and not the Firewire variant?

Cheers

Dennis

[Merlin66]

Dennis,
Thanks for that. That's interesting as I think the Mac OS X uses the firewire connection...
Let you know how I go...

[Merlin66]

Don't know where you got the original info, but I can say that the DMK21 firewire works 100% with PHD V1.10.0
In the list of cameras there's the choice " Imaging Source DCAM firewire" just select and off you go!!!
Hope this helps.

[Lester]

Thanks Merlin. I will not be trying this for some time till I get the Titan worked out and sat on the pier.

Are there different versions of PHD, that some may not be compatable with firewire?

[iceman]

I'm quite sure there are people using their DMK firewire with PHD successfully.

I'm even 95% sure I was guiding with my DMK firewire before I got my USB version.

I'll do some digging.

[Lester]

Thanks Mike.

Matthew Lovell informed me also that the firewire is compatable with PHD.