Imaging camera for a Lunt 100 Solar Scope.

[batema]

Hi,

A friend of mine (her school) has a lunt 100. She has asked me what imaging camera would be good for it. I have used a DMK 21 and the image is roughly a quarter of the sun. I have used a DMK 41 on it which produces an image of half the sun but when I put a 0.5 reducer on the camera I still just miss out on a full disc.

Could you please recommend an imaging camera for this magnificent scope as my knowledge in this area is limited.

Thanks

Mark

[pdalek]

DMK41 960 pixel vert @ 4.65um -> 4.46 mm
Lunt 100 focal length 800mm -> Image of sun about 7.5mm diameter.

A 0.5 reducer should work.
Check the reducer to camera distance against specs. You may need a spacer.

[batema]

Thanks Patrick. The lunt has a blocking filter 1800. I don't know if I should have mentioned that.

[pdalek]

Shouldn't matter - this is way bigger than the solar image at 800mm focal length.
Add a spacer between the reducer and camera. Provided you have enough focuser in-travel, you should get a full disk image.
How much extra distance is needed depends on the specific focal reducer.
For one example see
http://agenaastro.com/antares-1-25-0-5x-focal-reducer.html

[frolinmod]

Point Grey Grasshopper 3 GS3-U3-28S5M-C (USB3) or Grasshopper Express GX-FW-28S5M-C (Firewire-800) have large enough chips to just barely capture the whole solar disk without a reducer. Both are Mono, Sony ICX674 2/3", Global Shutter CCD, 1920 x 1440 at 26 FPS. I have the Firewire-800 version here, Firewire-800 being tried and true problem free technology, I chose it over USB3.

The current incarnation of the Lunt 100THa is D=102mm, F=7, FL=714mm. I have attached field of views for ICX205AL (DMK41), ICX274AL (DMK51) and ICX674.

[RD400C]

Mark
The link below is a great site for doing what you are trying to find out


http://www.12dstring.me.uk/fov.htm

[Paul Haese]

Don't use a reducer, you want detail. Use a barlow and a DMK51 or the biggest camera the ZWO optical make. It will give you a quarter with heaps of detail.

[pdalek]

The choice of camera really depends on what the user wants to see and how much they can spend.

You really don't have to worry too much about picking the exact sensor size to match the sun image diameter. There are cheap ways to scale the image.

Ordinary barlows can handle magnifying from 1.3x up. You will want this for sunspots, etc.
Ordinary reducers can do 0.9x down. Going much below f/4 is not ideal but is ok if great image quality isn't required.
The power of a barlow or reducer can be fine tuned by altering spacing.

The middle range about 1x can be done without too much difficulty. This is H-alpha, so forget chromatic aberration.
Ordinary spectacle lenses are cheap and can be finished to a suitable diameter. Anti reflection coating can be ordered. Use to make a weak barlow or reducer. The low power will not introduce much aberration.
For more money you can buy long focal length corrected doublets, negative and positive, which will work much better.

If this is for a school, as suggested in the original post, and a nice live view for a group audience is all that is needed, then high resolution may be wasted money.
The sun is 1962 seconds across, so 3s seeing ~ 654 pixel required. The display device probably will only have about 1000 pixels vertical.

If a live view isn't needed, then a 2x barlow and a red sensitive 1.6x crop DSLR will record a nice full disk image.

Observing in H-alpha is hard for many people. Maybe colour conversion is the main advantage in using a camera.

[Poita]

The point grey research cameras (Grasshopper Range) have better sensitivity and less noise than the imaging source cameras, I have used both for solar and the PGR cameras are definitely the way to go.

I currently have a grasshopper and GH3 camera in firewire 800.
The newer USB3 model can capture in 12bit mode at the same speed as in 8bit mode which the FW800 model cannot, so I would get the USB3 camera.
For that scope, get the biggest chip you can, you don't want to be reducing the disc optically, and mosaics are a pain in the bum!

If she has access to firewire800, then I can loan her a camera to try out. Most Macbook Pro and some imacs and mac minis have FW800 built in.

If they are using a desktop PC, I can loan out a FW800 PCIe card as well.

[Paul Haese]

Agreed Peter. I would have recommended a PGR camera as I have been using those for 5 years now, but the budget for these is not for everyone. Currently using the 9mp camera, not without its issues and I wonder if I need a bigger blocking filter than the 1800.

[batema]

Thank you all for the advice. The computer is just a basic school Dell 4.00Gb Intell Core i5 and 32 bit operating system. Given that I can not find the cost of a grasshopper flea and i have no idea which one would suit. Could someone please tell me what grasshopper I should get/tell the school. It is something they will put into their request budget. If you can tell me the price or direct me to the page that would be great. I will suggest a DMK 51 and could someone suggest a good barlow.

Thank you

Mark

[renormalised]

Here's the page for the Grasshopper...

http://grasshopper3.ptgrey.com/USB3/Grasshopper3

and the page for the Flea...

http://ww2.ptgrey.com/USB3/Flea3

and the direct from factory store, online...

http://www.ptgreystore.com/usb-30

[Paul Haese]

I am using the 9mp camera but I think the 6 will suit most situations. The 9 is too big for a 1800 BF. The half inch sensor vignettes (I think; trying to sort this out at present) on that BF.

[batema]

Paul if they got the GS3-U3-60S6M-C
<LI value=1 madcap:autonumposition="none">Sony ICX694 CCD, 1", 4.54 µm<LI value=2 madcap:autonumposition="none">Global shutter<LI value=3 madcap:autonumposition="none">2736 x 2192 at 13 FPS
Would that be good for the Lunt and would this camera work on the computer they will use mentioned above. It says I have to register to get the price???

Thank you

Mark

[Paul Haese]

Couple of things.

First the USB3 big format cameras need a SSD for recording the data on. I am using a 250gig drive.

Second, you need a fair bit of RAM. I am using 16gig of RAM.

Next, i5 is ok but i7 is preferred. You can use 32bit, but a new machine will give you 64 bit and flawless performance. The costs may be prohibitive.

[batema]

Thank you. I think I should suggest a DMK 51.

[frolinmod]

That's correct. In order to see pricing in the Point Grey online store you first need to register as a user there. It's trivial to do and anyone can do it. No problem at all.

Oh my, you picked an expensive one:

[batema]

That definitely ends the point grey option.