Data gathering rate query?

[bomberbaz]

Hello folks, just looking for a little help and advice here.

I am "considering" upgrading from my current budget entry evoguide and moving up to a WO ZS 61.

Rationale being It is a dedicated piece of kit with superious glass (All FPL53) and has a bigger aperture, providing around 50% more light gathering than my current scope.

Also as it is F5.9 rather than F4.8 it gives a smaller FOV which I want to get tighter images of many DSO's, here is where my head gets a little dizzy.

At F4.8 but only 50mm aperture the area of sky covered by the evoguide is double that of the Zenithstar. So it is faster at gathering light but slower because it is a smaller aperture and also gathering light over a larger area. (see image below)

However the Zenithstar at F5.9 is slower but faster as it opposite to the above. 

I am wondering will the slower ZS 61 be worth the additional cost. 

Another option is barlowing at 1.6 the evoguide which would give you the same FOV as the ZS but slower at 7.7. << I think this statement here kind of tells me the answer but I still don't quite get why, I find this all rather confusing. 

Can anyone give me a "very" simple overview to help me manage my expectations and decide if it is worth the upgrade.

If I did upgrade, it would also put me right on the weight limit too. 

Edited May 15, 2022 by bomberbaz

[Fegato]

I'm not really an expert, and I'm not really a refractor person either (although I do use an evoguide 50ED for guiding), so whether this is any use, I don't know!

For imaging, the FOV is driven purely by the focal length and your sensor size (assuming no issue with size of imaging circle for the particular scope). So in simple terms, the WO at 390mm has a smaller FOV than the 50ED at 242mm for the same camera. 

From there, the F Ratio varies based on the aperture of the scope. So for the same focal length, larger aperture means smaller F ratio. The point here is that the F Ratio doesn't determine FOV, it's a measure of the "speed" - and it's the combination of focal length and aperture that determines this. The WO is "slower" because the focal length / aperture is slightly higher than the 50ED.

I can't really comment much on the upgrade I'm afraid. Both scopes get good reviews for what they are, although the WO is certainly designed for imaging rather than guiding, so might be preferable. Beyond your preferences for FOV and speed, I guess it's down to the optics. One would assume the WO would be better on that score, if only based on price. Hopefully someone with first hand experience can provide some better info on that!

 

[bomberbaz]

3 hours ago, Fegato said:

I'm not really an expert, and I'm not really a refractor person either (although I do use an evoguide 50ED for guiding), so whether this is any use, I don't know!

For imaging, the FOV is driven purely by the focal length and your sensor size (assuming no issue with size of imaging circle for the particular scope). So in simple terms, the WO at 390mm has a smaller FOV than the 50ED at 242mm for the same camera. 

From there, the F Ratio varies based on the aperture of the scope. So for the same focal length, larger aperture means smaller F ratio. The point here is that the F Ratio doesn't determine FOV, it's a measure of the "speed" - and it's the combination of focal length and aperture that determines this. The WO is "slower" because the focal length / aperture is slightly higher than the 50ED.

I can't really comment much on the upgrade I'm afraid. Both scopes get good reviews for what they are, although the WO is certainly designed for imaging rather than guiding, so might be preferable. Beyond your preferences for FOV and speed, I guess it's down to the optics. One would assume the WO would be better on that score, if only based on price. Hopefully someone with first hand experience can provide some better info on that!

 

No your explanation makes good sense thanks. I am actually looking at another option but FL and aperture is the same, but around 500g lighter which makes a big difference in this instance.

tHANKS.