Choosing an FF/FR for an FLT110

[haitch]

Amongst my arsenal is a W.O. FLT110 (just the TMB designed one) that came with the matched 1.0x Flattener however I'd like to bring it down from it's native f7 for a few snaps. As far as I can make out the suggested WO option is the PFlat 6 but I've struggled to find one and it looks like it was rather expensive when it was available new.

Anyway, whilst I've been waiting for the right combination of time, energy and clear skies I've picked up a few FF/FRs to try out. The latest is a TV TRF2008 which came at the right price even though it may not be a good match so I shouldn't lose much if/when I pass it on.

Now the TV says it is designed for scopes from 400-600 focal length but I was thinking surely its not the f/l of the scope that matters but f ratio? Surely any 2 scopes at, say, f7 would have the same shaped light cone? Or am I oversimplifying things?

Teach me about optics... 🤓

[Guest Vangelis]

I suggest you try out Altair Astro.  I bought one for my Esprit 120 half the price of the Skywatcher flattener but I wanted a reducer.  Cost me £99. To be honest unless you zoom in or start putting it through tools like ccd inspector etc I can't for the life of me think why the casual observer wouldn't be happy with it.  Heres M42 albeit a compressed jpeg. Taken with this very reducer. I wouldn't spend hundreds of pounds on one for a minimal tidying up of stars on the edge of frame.

[haitch]

That looks pretty decent to me (and my admittedly untrained eyes) if anything I'd say it was slightly over correcting at the edges - have you had a play about with the spacing?

PS - what size sensor is that?

Cheers

[Guest Vangelis]

Hi. According to the specs the spacing is already ok. Just screws onto my t ring and camera goes into focuser. It's a crop sensor aps-c chip. As far as I'm aware I cannot reduce the length of the reducer. 

[geordie85]

Have you thought about putting an ad in the classifieds section? I recently got a WO Flattener 4 for a bargain price of £85.

[ollypenrice]

What is your precise objective in looking for a reducer?

Olly

[haitch]

Hi Olly, just to allow slightly wider fields and collect photons a bit quicker. The dedicated flattener I’ve got purportedly gives a flat field over a 35mm image circle so perhaps a bigger sensor is what I should be looking at 🤑

Edited June 16, 2019 by haitch

[ollypenrice]

The wider FOV makes perfect sense though, as you say, a bigger chip will do that. The speed is a moot point. If you want all of the new FOV in the final image then the reducer will bring you to an acceptable S/N ratio faster but, if you are going to crop out a target of now reduced size on the chip, the F ratio myth applies.

Olly