Focal Reducer?

EzyStyles (Eric) · #1 21-03-2006, 11:44 AM

Hi Guys,

I have a 8" F/4 scope and was wondering should I get myself a focal reducer for a wider field? or is there another method? for astrophotography.

What are the negative/positive effects?

im stuck atm

Striker (Tony) · #2 21-03-2006, 12:08 PM

I'm with Geoff on this...reducing a F4 scope down with a focal reducer will probably give you a huge amount of Coma.

If you had say a f7 scope reducing it down to F5 then that wouldn't be a problem..the problem is your scope is fast enough as is.

Ed80 is the way to go....a quality focal reducer would cost a packet anyway...ed 80's are going cheap now a days.

If money is the problem...save for the ED80 instead of wasting your money on a focal reducer that your not going to be happy with any way.

janoskiss (Steve H) · #3 21-03-2006, 12:32 PM

A DSLR would give you a wider field than the DSI. Roughly about 1.5 degrees.

ving (David) · #4 21-03-2006, 12:42 PM

like steve said, maybe you should consider a dslr as your next purchase

f/4 is already very fast!

EzyStyles (Eric) · #5 21-03-2006, 04:00 PM

Thanks for the advise guys. now thinking DSLR or ED80.. broke.. broke...

davidpretorius · #6 21-03-2006, 04:22 PM

sorry mate, get both!!! double broke.

That is where I will be going eventually, a canon 350 etc and a ed80. What these guys can produce is breathtaking!!!

ving (David) · #7 21-03-2006, 04:39 PM

Quote:

Originally Posted by EzyStyles

Thanks for the advise guys. now thinking DSLR or ED80.. broke.. broke...

you do of course realise that an ed80 has a higher f/ratio than your f/4 reflector dont you?

janoskiss (Steve H) · #8 21-03-2006, 05:18 PM

Yes, ED80 has higher f-ratio, but shorter focal length, which is what determines the true field of view for photography. Though it is not that much shorter at 600mm than the 8" f4 at 800mm. But no coma, so quite a bit larger usable field I'd expect.

But maybe the new Saxon EDSP 80mm is what you need, Eric. It looks like it is shorter than the older style ED80, and has a much better focuser.

Starkler (Geoff) · #9 21-03-2006, 06:28 PM

Ezy , it seems apparent that you have a passion for dso photography , so the dslr is in your destiny anyway

Not knowing alot about the dark side of the hobby (photography), I imagine you would be less limited by the newt/dslr compared to the ed80/dsi combo in the meantime.

The ed80 has a focal length of 600mm, compared to 800mm for your newt, so you would get a 33% wider field but with much slower photon collecting.

Now how much bigger is a dslr ccd chip compared to the DSI ?

EzyStyles (Eric) · #10 23-03-2006, 04:47 AM

Thanks for the reply all. Can't buy both. well not now until i save

I guess if a digital SLR can make a great difference with 'wider field of view' and quality pics so be it. Plus the DSI i think is maxed out now. Can't really do much with it. I was also thinking of DSI 2? larger ccd chip, better cooling etc etc. Since now im use to the software to it already.

DSI 2 - $899
Canon 350d - $859 (from friend brand new)

which one?

Cheers

ving (David) · #11 23-03-2006, 09:37 AM

Quote:

Originally Posted by janoskiss

Yes, ED80 has higher f-ratio, but shorter focal length,

duh!
god i am thick sometimes!

I should steer clear of imaging related threads!

davidpretorius · #12 23-03-2006, 12:59 PM

first reaction - canon!!!

i must admit 4 weeks ago, i would not have questioned this, but i am very impressed with what the dsi can do and hence what the dsi2 can do.

unfortunately you are our dsi man and therefore i don't know how to advise.

I do know I am extrememly impressed with the canon crew on IIS. fantastic sharp images.

So second thoughts canon again!

asimov (John) · #13 23-03-2006, 01:06 PM

As Davo said.

avandonk · #14 23-03-2006, 02:53 PM

Focal reducers work fine with the smaller sensors as the DSI. The field is to small to for field curvature or coma to be a problem. I would go so far to say that even a focal reduction of 0.5 which in your case would be 400mm at F2.0 would be fine. The 1 1/4" type focal reducers that screw into the 1 1/4" nosepiece of the DSI.

Bert

EzyStyles (Eric) · #15 23-03-2006, 06:10 PM

Quote:

Originally Posted by davidpretorius

first reaction - canon!!!

i must admit 4 weeks ago, i would not have questioned this, but i am very impressed with what the dsi can do and hence what the dsi2 can do.

unfortunately you are our dsi man and therefore i don't know how to advise.

I do know I am extrememly impressed with the canon crew on IIS. fantastic sharp images.

So second thoughts canon again!

Go on Dave, i know you want a DSI. Just $500. c'mon

i can always sell you mine and get the canon

EzyStyles (Eric) · #16 23-03-2006, 06:12 PM

Quote:

Originally Posted by avandonk

Focal reducers work fine with the smaller sensors as the DSI. The field is to small to for field curvature or coma to be a problem. I would go so far to say that even a focal reduction of 0.5 which in your case would be 400mm at F2.0 would be fine. The 1 1/4" type focal reducers that screw into the 1 1/4" nosepiece of the DSI.

Bert

wish there is a blockbuster for astro gear. really think it will do the trick? cos Bintel is really close to my house

janoskiss (Steve H) · #17 23-03-2006, 06:31 PM

If Bert says it will work, it will work.

Just forget about the rest of the posts, Bert is the only one here who has a clue about these things.

avandonk · #18 23-03-2006, 07:55 PM

If you can tell me the distance between the sensor and nosepiece of the DSI I most probably have a lens which will do the job for nix. The futher the lens is from the sensor the higher the reduction.

I use one with my guidescope and toucam to make the 600mm guidescope into a 320mm one.

Bert