Focal reducers

[John]

50 minutes ago, globular said:

If you’d drawn the 32mm with reducer compared to a 50mm without the reducer then they would have given near identical fov, mag and exit pupil....

Which 50mm ?

[Franklin]

2 hours ago, John said:

Which 50mm ?

I thought it was 40mm?

IMO reducers are for cameras/imaging purposes.

If wanting lower powers and wider fields visually then get a faster scope and/or longer focal length eyepieces.

[Franklin]

15 hours ago, Bugdozer said:

I did wonder how long it would be before the inevitable "buy a new telescope" comments turned up!

F/7 scopes are a good middle ground, a compromise and make great all rounders.

[globular]

5 hours ago, John said:

Which 50mm ?

Any. How about the superview…

https://www.firstlightoptics.com/stellalyra-eyepieces/stellalyra-50mm-2-superview-eyepiece.html

 

p.s. I”m not suggesting a 50mm is a good idea. Just that for any EP + reducer that is considered there is an EP that will give similar results without the reducer.

Edited October 26, 2023 by globular

[badhex]

48 minutes ago, globular said:

Any. How about the superview…

https://www.firstlightoptics.com/stellalyra-eyepieces/stellalyra-50mm-2-superview-eyepiece.html

 

p.s. I”m not suggesting a 50mm is a good idea. Just that for any EP + reducer that is considered there is an EP that will give similar results without the reducer.

I was concerned for a moment that the 50mm might make some outrageous claim about AFOV since the 30mm is supposed to be 68° which is not possible at 50mm in a 2" barrel AFAIK - but it turns out that the 50mm is only 48° which I believe is fine. 

I have the 30mm and do not rate it in a fast scope as the edge performance is not good, but in an F10 I guess it's probably fine. I do not know for certain but I wonder if the 50mm is the same in that regard. I don't know if the design is the same in both but if so I believe the "super plossl" is essentially an additional 5th lens, perhaps like and Erfle. 

All of this said: as everyone stated above, the 50mm will have vignetting and potentially isn't perfect in the outer field of view but since this is about maximising exit pupil at the cost of the edge anyway, it will give a 5mm exit pupil which may work well for the use case, and it's relatively cheap. I personally would not buy another superview based on my experience with the 30mm though, but that's because I primarily use 2" format scopes at F7 or faster. It is not great in an F6! 

Edited October 26, 2023 by badhex

[John]

It was a long time ago but I went down both the FR route and then the 2 inch eyepiece route when I owned Celestron C5's and then a C8. I felt more comfortable with the C8 in 2 inch mode due to tube balance etc.

I think I did try both the GSO Superview 42mm and 50mm eyepieces (same as the Stellalyra's) in the C8 setup - I was on a "going wider" quest as well at the time !

I then picked up a 8 inch F/6 dob and moved away from SCT's. Had to move to better eyepieces then of course 😉

I did try some interesting things in the back of SCT's back then 😁

 

 

Edited October 26, 2023 by John

[Bugdozer]

Thank you everyone who has answered what I was asking about, which was focal reducers. My conclusion is that I won't know until I get one and try it because there are too many variables. 

 

[vlaiv]

1 minute ago, Bugdozer said:

Thank you everyone who has answered what I was asking about, which was focal reducers. My conclusion is that I won't know until I get one and try it because there are too many variables. 

 

Btw what scope is this and what focal reducer are you considering using?

[Bugdozer]

2 minutes ago, vlaiv said:

Btw what scope is this and what focal reducer are you considering using?

The information you need is in the OP. I am not considering using any particular focal reducer, I wanted to understand what the negative aspects of using one might be. The main negative aspect appears to be people saying "if you're considering a focal reducer then you have the wrong telescope". I suppose we could say that to everyone using a Barlow lens too - instead of a Barlow, use a scope with a longer focal length! 

[vlaiv]

On 25/10/2023 at 00:12, Bugdozer said:

I currently have an f/10 5" scope.

That is not saying very much.

It can be refractor, reflector, SCT or even MCT with those specs (although I've only seen F/10 Maksutov in form of photo lens).

3 minutes ago, Bugdozer said:

The main negative aspect appears to be people saying "if you're considering a focal reducer then you have the wrong telescope". I suppose we could say that to everyone using a Barlow lens too - instead of a Barlow, use a scope with a longer focal length! 

Main negative aspect can be that you don't get what you are hoping to get with focal reduction, but that really depends on what scope you have, what focal reducer and what you intend to do with it.

For example - I've mentioned that I have x0.67 focal reducer. I've primarily intended that for imaging use.

There are some people that find this focal reducer not usable for that exact use case (same scope, same focal reducer) - because they want to use it with too large sensor. Scope simply does not provide corrected field large enough to cover large sensor after "squeezing" of the field.

On the other hand - I'm using that reducer happily on refractor telescope for visual with particular eyepiece. It might not work as good with different eyepiece though.

I even used said focal reducer on my 4" Maksutov - because I tried with very small sensor that I knew won't vignette although back port on 4" Mak is very small.

Besides these issues - focal reducer can amplify optical problems if is not suitable for particular telescope design or is used on very fast optics.
For example - I tried very strong x0.5 focal reducer for EEA with F/5 fast achromat. Results were horrible - stars were distorted and I was even not able to bring them to focus properly. On the other hand, same focal reducer worked very very well in EEA role with F/6 newtonian with very small sensor.

[badhex]

53 minutes ago, Bugdozer said:

Thank you everyone who has answered what I was asking about, which was focal reducers. My conclusion is that I won't know until I get one and try it because there are too many variables. 

45 minutes ago, Bugdozer said:

The information you need is in the OP. I am not considering using any particular focal reducer, I wanted to understand what the negative aspects of using one might be. The main negative aspect appears to be people saying "if you're considering a focal reducer then you have the wrong telescope". I suppose we could say that to everyone using a Barlow lens too - instead of a Barlow, use a scope with a longer focal length! 

Apologies for the drift into EP discussions, though often people will try to help solve your root challenge (in this case increasing exit pupil size and/or TFOV) if not always the specific question asked - I would take this as a sign of people just trying to be helpful 🙂

I think maybe the takeaway should not be that you are using the wrong kind of scope, just that reducers can sometimes come with caveats that may mean you're trading one issue for another (which may be an acceptable outcome as noted). This may be especially true for SCTs/Maks (which I'm going to guess you are using - is it a C5?) since there have been many discussions on SGL about using reducers with the C5 vs changing to a 2" visual back to try and maximise both exit pupil and TFOV. I asked a very similar question a couple of years ago, if you're interested, linked below. I definitely recommend reading at least the link http://www.waloszek.de/astro_ce_c5_2z_e.php which @vlaiv supplied in my post, it's really interesting and might give you some ideas about getting more out of your C5 if you wanted to go that route.

Finally I would also suggest that you are right about not necessarily knowing until you try it! IIRC @Ags has used and enjoyed the Celestron 0.63x reducer on a C6. Like eyepiece preference, every experience can be quite different depending on the person.