Hi all,
since the introduction of optical trains, as far as I can see, I always have a wrong focal lenght reported in my capture window.
It seems the software is just ignoring my 0.67x reducer. It comes up with a focal lenght of 670mm which is the native one, but I declared 420 which is the reduced one, and the text is thus in red.
Pixinsight, when examining my pics, comes up with the right focal lenght, so I'm not sure what's going on.
Am I supposed to enter the focal lenght of the telescope itself and ignore the reducer? If so, it's a bit confusing.
Thanks

Your optical train specifies 0.67 reducer?

Yes it does, it's even reported in the capture window.
Is there something else to maybe specify somewhere?

Hi Fabio,

I tried replicating your issue on the Sims...


Here I setup an Optical Train with a 670mm FL scope and a 0.67 reducer. Then solved in the Align tab for this OT. The reducer (0.67x) is shown as is the telescope FL of 650mm which matches what the solver sees.

Next I took a sub in Capture.


The FocalLength of the sub is 670 * 0.67 = 448.9 which is what is expected.

Can you share similar screenshots of what you're getting?

Hi John,
the issue I thought I was having is that I expected to see the effective reduced focal lenght in the capture window, instead of the non reduced, native one.
The text was red because the focal lenght is not what the manufacturer reports but it's only slightly off.
Once I enter the correct focal lenght, it should be fine.
Maybe it would help if the FL field would somehow indicate it's the native one, not the effective one.

Thanks!

Same here, I found it confusing, too.

HI Fabio,

Thx, just so I'm clear... when you say "capture" are you referring to the Align window which is the window in my screenshot?

If so, I could change:
1. The tooltip to make it clear that the FL and F/ fields exclude any reducer, or
2. Display the "reduced" FL and F/ in these fields that is appropriate for the telescope and reducer.

Since this has been this way for a long time, doing 2 will doubtless cause confusion with folks who have grown accustomed to the current convention. In addition, it would complicate the situation where the user wishes to adjust the FL in the Optical Train based on the solve feedback. Currently, they can simply type in the displayed value. If I did change 2 they would have to calculate the effective FL of the telescope manually and apply that.

So 1 would probably be better.

Would welcome any comments.

John,

this is my 2 cents... When I see FL or F/ alone, I always expect it to refer to FL(eff) or FL(train). Same with F/.

In "solution coordinates" the FOV result refers to the train's FOV, so I would even more expect all other values like FL and F/ to refer to the active optical train, too. To avoid any confusion I'd label it FL(eff) or FL(train).
I can see where you're coming from with regard to manually setting the FL in the train. Why not (optionally) auto-update this field so nobody would have to do it by hand?

Alternatively, you could display both values, FL(eff) and FL(telescope) as well, maybe replacing the R: field which would no longer be needed.

John,

To add to the discussion. The reducer thing has been so confusing to me that I have simply set up 3 different optical trains with different focal lengths and have not used the reducer field. One of the trains if for the scope at it's native focal length (2800mm), one using a .7 reducer (1956mm), and one for when I use a HyperStar (540mm).

I understand the concern regarding confusing people already used to this but the optical train feature is relatively new and this seems to cause confusion and frustration for new users (and some not so new users!).

Thanks

Hi John,
yes, I said capture but I really meant the same window you posted, so align.

I don't know how best to solve this. The tooltip would already be something, but to be honest with you, I think how it is now is a bit backwards.
The focal lenght is, to me, the result of all your optical train. The information given there is just not useful for the situation you're in. I agree that the telescope must be defined correctly, but in the align window I'd expect to see the data pertinent to what I'm imaging. Actually, this information is completely missing.

I get what you say about people getting used to it. But man, I'm 20 years into this hobby and I couldn't figure this out. Maybe adding the info somewhere would serve both needs?

Thanks anyway for clearing things up!

I changed the tool-tip to this: Active telescope raw (effective) focal length in millimeters. This is the raw focal length without any reducers or barlow. The effective focal length is measured from plate-solving.

The reason it was configured as such is that the user shouldn't calculate the focal length manually, so they get to see raw FL and whatever reducer/barlow they have active in the optical train.

Ok nevermind my previous message. I changed everything to reduced values in 3.6.6 GIT. So all values now take reducer/barlow into account.