Short focal length scope and Mathematica Astronomica

[Ratlet]

I'm not quite sure how it works.  I mean I originally started looking at whether a 0.6x reducer would work to get a really nice short focal length for my 102ed f7.

Why am I now looking at whether it would be a better idea to get something like a 1x or 0.8x reducer for a longer fov and instead getting a 72ed type scope which gives me a wider fov natively.

Is there a reasonable priced 72ish ed scope that'll do good visual and imaging and play well with a generic field flattener?  Ideally with minimal colour on stars that'll work with an autofocusser (my understanding is my vintage glass will not due to how the takumars focus different frequencies of light).

I feel like I'm asking to be talked back from a new scope ledge, but I'm also aware that I'm asking in a forum that I know love nothing more than helping people spend their money lol

[Elp]

Askar 71F.

[Elp]

I know what you mean, the SF102 is a very odd FL, don't know how people get on with it. It's a bit short to get those tiny targets, and too long to get those popular ones full size. I've kind of resigned mine to visual use because of it, mosaics can be a pain, but would be much higher resolution if I decided to do it with the 4 inch.

It's one of the reasons I like my Z61 so much, I can still see small objects however tiny they may be, but I can guarantee you they'll be sharp, and imaging larger targets in full view are also in reach, with my x0.65 reducer however much it may be, I also get Redcat beating FOV.

 

Edited August 8 by Elp

[Ratlet]

53 minutes ago, Elp said:

I know what you mean, the SF102 is a very odd FL, don't know how people get on with it. It's a bit short to get those tiny targets, and too long to get those popular ones full size. I've kind of resigned mine to visual use because of it, mosaics can be a pain, but would be much higher resolution if I decided to do it with the 4 inch.

It's one of the reasons I like my Z61 so much, I can still see small objects however tiny they may be, but I can guarantee you they'll be sharp, and imaging larger targets in full view are also in reach, with my x0.65 reducer however much it may be, I also get Redcat beating FOV.

 

Yeah, it's an odd focal length but not a million miles from the 130pds.  Once I get home I'm going to have a scan through the images on there to see what targets are viable.  I know it's a great focal length for M27 and I got a nice one of Stephens Quintet.

Think it might be better to play to the scopes strengths rather that try to make it do something it's not.

Also a lot of the objects that will fit the star field with a 0.6x reducer will fit, they won't be framed particularly well.

[PeterC65]

I have the StellaMira x0.6 reducer which I use with my TS Optics Photoline 72 Apo. It certainly increases the field of view but doesn't flatten the field very well. Partly because of this I now have an Askar FMA135 for really widefield (EAA only).

I also have the StellaMira x1.0 field flattener which does further flatten the already fairly flat field of the Photoline 72.

I think that x0.6 is pushing things a bit for a reducer / field flattener so you may find that it doesn't work so well with your Starfield 102.

I have a different dilemma in that I don't have a Starfield 102 but keep hankering after one. It's performance as standard would be very similar to my Explorer 150 I think (similar focal length, smaller aperture but without the central obstruction, slower for EAA), and with the x0.6 reducer, similar to the Photoline 72 (similar focal length, but bigger aperture and faster). So far I've resisted the temptation.

If you do decide to go for a smaller Apo then I'd recommend the TS Optics Photoline 72.

 

 

[Ratlet]

2 hours ago, PeterC65 said:

I have the StellaMira x0.6 reducer which I use with my TS Optics Photoline 72 Apo. It certainly increases the field of view but doesn't flatten the field very well. Partly because of this I now have an Askar FMA135 for really widefield (EAA only).

I also have the StellaMira x1.0 field flattener which does further flatten the already fairly flat field of the Photoline 72.

I think that x0.6 is pushing things a bit for a reducer / field flattener so you may find that it doesn't work so well with your Starfield 102.

I have a different dilemma in that I don't have a Starfield 102 but keep hankering after one. It's performance as standard would be very similar to my Explorer 150 I think (similar focal length, smaller aperture but without the central obstruction, slower for EAA), and with the x0.6 reducer, similar to the Photoline 72 (similar focal length, but bigger aperture and faster). So far I've resisted the temptation.

If you do decide to go for a smaller Apo then I'd recommend the TS Optics Photoline 72.

 

 

I don't think you'll be too far off with your assesment of the performance of the 102ed.  I've got the 130pds and would say it performs better than the 102ed.  That is me comparing by memory, and it has been a while since I took the 130pds out for summer targets.

Actually that might be a good shout as a project, to take out them both and give them a compare.

Once I get some free time I'm going to sit down with stellarium and do some comparison on different scopes and rescuer/flattener combos and also trawl the 130pds post for good targets for the 102.

This far though my imaging has been much closer to eaa than proper astrophotography.  I basically use it to get views my eye can't, but rather than live stack I just rack up the images and deal with them in the morning.

The other option I've got is to try and figure out if I can get autofocus to work with my vintage glass.  As I understand it perfect focus with takumars lenses will give red halos so you need to back off slightly.  You essentially have all colours defocused slightly but equally.  The stars are a tiny bit bloated but it looks pretty darn good when you hit the sweet spot. 

[ollypenrice]

I think a 0.6x reduction on an F7 scope is a big ask. It comes down to F4.2. There are a few refractors as fast as this at 4 inches but they are very expensive ones and designed for this F ratio from the ground up.

Olly

[Ratlet]

@ollypenrice I'm going to go down the 0.8x route and couple it with a short focal length scope (60 or 70mm) when I can afford it.  Quite like the photoline as it keeps the stable looking consistent.  My DSLR has sat doing nothing for over a year now so I've ordered a replacement UV/IR enhanced spectrum filter from AliExpress and I'm going to  Astromodify my DSLR.  It's only £15 for the filter and will allow me to do get better response from Nebula, a wider field of view and still be usable for normal photos.  It's a t3i so quite out of date (so I won't lose much if I break it) but the times I used it I was happy enough with the images.  It will also give me a cloudy night project.

So that is the plan for now.

Edited August 13 by Ratlet