30 replies to this topic

[morrocoy]

Hello everybody,
thank you for accepting me in this wonderful group (I'm italian), I just gave my daughter a Celestron Starsense Explorer DX 130 AZ (reflector newtonian telescope) and we are having a lot of fun.
I have read a lot about eyepieces and would like to buy zoom eyepiece.

The major limit of zooms is not having a wide FOV especially at small magnifications and not even constant.

I have divided the zooms to have into three groups:
1 - from 2mm to 8mm
2 - from 8mm to 20mm
3 - from 20mm to 40mm

 

For the first group i found this (from 3mm to 6mm with constant FOV=50°) https://www.televue...._page.asp?id=49

For the secon group i found this (from 7.7mm to 15.4mm with constant FOV =75°) http://apm-telescope...I_aIRMEKu6b8lcM

For the third group I have not found anything, do you have any suggestions?

 

Surely the cost of such a set is important.

 

Opinions? Ideas?

 

Thanks

 

[SeattleScott]

Hello everybody,
thank you for accepting me in this wonderful group (I'm italian), I just gave my daughter a Celestron Starsense Explorer DX 130 AZ (reflector newtonian telescope) and we are having a lot of fun.
I have read a lot about eyepieces and would like to buy zoom eyepiece.
The major limit of zooms is not having a wide FOV especially at small magnifications and not even constant.
I have divided the zooms to have into three groups:
1 - from 2mm to 8mm
2 - from 8mm to 20mm
3 - from 20mm to 40mm

For the first group i found this (from 3mm to 6mm with constant FOV=50°) https://www.televue...._page.asp?id=49
For the secon group i found this (from 7.7mm to 15.4mm with constant FOV =75°) http://apm-telescope...I_aIRMEKu6b8lcM
For the third group I have not found anything, do you have any suggestions?

Surely the cost of such a set is important.

Opinions? Ideas?

Thanks

There isn’t anything for the third group. It isn’t really practical. Zooms aren’t wide enough to get into those longer focal lengths. There is the SVBONY 10-30 but the AFOV gets really small at 30mm. Even with the BHZ, the field of view at 24mm setting is essentially the same as 20mm, so you aren’t getting any wider by dropping down to 24mm (really 22.5mm).

There is a simple solution though. Zoom eyepieces are built for birdwatching/spotting scope users. Which is a much larger market segment than stargazing. And they only need 1.25” or similar formats. All you have to do is get as many people into stargazing, and stargazing with zooms rather than fixed eyepieces, and a 2” zoom with longer FLs should soon appear in the market.

Scott

[LDW47]

There isn’t anything for the third group. It isn’t really practical. Zooms aren’t wide enough to get into those longer focal lengths. There is the SVBONY 10-30 but the AFOV gets really small at 30mm. Even with the BHZ, the field of view at 24mm setting is essentially the same as 20mm, so you aren’t getting any wider by dropping down to 24mm (really 22.5mm).

There is a simple solution though. Zoom eyepieces are built for birdwatching/spotting scope users. Which is a much larger market segment than stargazing. And they only need 1.25” or similar formats. All you have to do is get as many people into stargazing, and stargazing with zooms rather than fixed eyepieces, and a 2” zoom with longer FLs should soon appear in the market.

Scott

The Svbony 10-30 zoom in that scope at 30mm puts out a 22x, 1.5° TFOV not exactly really small !

[LDW47]

Hello everybody,
thank you for accepting me in this wonderful group (I'm italian), I just gave my daughter a Celestron Starsense Explorer DX 130 AZ (reflector newtonian telescope) and we are having a lot of fun.
I have read a lot about eyepieces and would like to buy zoom eyepiece.

The major limit of zooms is not having a wide FOV especially at small magnifications and not even constant.

I have divided the zooms to have into three groups:
1 - from 2mm to 8mm
2 - from 8mm to 20mm
3 - from 20mm to 40mm

 

For the first group i found this (from 3mm to 6mm with constant FOV=50°) https://www.televue...._page.asp?id=49

For the secon group i found this (from 7.7mm to 15.4mm with constant FOV =75°) http://apm-telescope...I_aIRMEKu6b8lcM

For the third group I have not found anything, do you have any suggestions?

 

Surely the cost of such a set is important.

 

Opinions? Ideas?

 

Thanks

The Svbony 10-30 zoom is a quality built, excellent performer for its price of less than $100, if you can find one in stock !

 

Edited by LDW47, 08 April 2021 - 12:12 PM.

[SeattleScott]

The Svbony 10-30 zoom in that scope at 30mm puts out a 22x, 1.5° TFOV not exactly really small !

Really narrow AFOV though. That works out to what, 35 AFOV or something?

[cst4]

Not much options on zooms that cover your 3rd group you list from 20mm to 40mm.  However, I would say you do not actually need a zoom at all for this range.  Going from 40mm to 20mm in your scope would be from 16X to 32X magnifications, which is not really that much of a jump at all.  Most people on here say that you should stay above about 35X anyway with any scope that has a secondary spider to ensure you do not get a shadow of the spider in the view.  So many might not even use an eyepiece in this range at all with your scope.  I think I would just try to find one eyepiece with a decently wide AFOV in the 20mm to 26mm range and that be it.  Something like a 24mm ES 68 or 25mm XCel-LX would probably do well.

 

If I had that scope I would likely use eyepiece around 25mm, 12mm, 8mm, 5mm, 3.2mm.  Zooms are the most beneficial at lower focal lengths where they cover all your mid to high power needs... the 3mm to 6mm TV zoom would be nice and would cover a large range.  The mid-range zoom you list would get you from about 42X to 84X magnifications.  Again that is not a large jump at all... You would likely find you would use the shortest and longest focal length settings and skip everything in between, which kind of negates the point of a zoom.  One or two fixed focal length pieces would also get the job done just as well here in this range.

[Jeff Morgan]

For the third group I have not found anything, do you have any suggestions?

 

 

Nothing made for your Group 3.

 

Get the upcoming APM Zoom + barlow to cover Groups 2 and 1.

 

Then a regular eyepiece in the 30-35mm range.

[thecelloronin]

Even with the BHZ, the field of view at 24mm setting is essentially the same as 20mm, so you aren’t getting any wider by dropping down to 24mm (really 22.5mm).
 

24mm does have its uses though, such as an additional .75mm of exit pupil. (Well, I guess that's one very limited use.)

Edited by thecelloronin, 08 April 2021 - 02:52 PM.

[Spile]

I supplement my Baader Hyperion IV zoom and Barlow with a 42mm wide angle EP.

[SeattleScott]

Typically yes you will want one or two low power eyepieces to compliment a zoom because they just don’t go very wide. Could do a 40mm SWA with a 20-25mm UWA, then switch to the zoom under 20mm. Something like that.

Scott

[thecelloronin]

I use the 22T4 on my 10" dob for low power. I used rings to parfocalize the Baader zoom at 16mm and added some loop-end velcro on the barrel as a tactile cue so that I can always jump down to what I consider the lowest useful range of the BHZ. Pics here: https://www.cloudyni...n-zoom-dioptrx/

 

Pretty much happy with this setup. Only really use lower powers than the nagler for filters and certain larger objects.

[LDW47]

Really narrow AFOV though. That works out to what, 35 AFOV or something?

But is the TFOV not the one that counts, what your eye actually sees ? What am I missing ?

[SeattleScott]

But is the TFOV not the one that counts, what your eye actually sees ? What am I missing ?

The TFOV is dependent on the scope. 35 AFOV might suffice for an 80mm Apo for viewing Double Cluster, but not so useful for 8” Dob or SCT. Also, 1.5 degrees can’t do justice to Pleiades. Borderline at best for Beehive. So you miss out on some of the precise targets that one gets an 80mm Apo for because of the narrow AFOV.

1.5 degrees is nice. 3.0 degrees is better.

Shoot, I get 1.4 degrees with my 6” Mak using my 42mm 65 AFOV. If I couldn’t go wider with an 80mm Apo than with a F12 Mak, why in heavens name would I want an 80mm Apo??

Scott

Edited by SeattleScott, 08 April 2021 - 06:37 PM.

[LDW47]

The TFOV is dependent on the scope. 35 AFOV might suffice for an 80mm Apo for viewing Double Cluster, but not so useful for 8” Dob or SCT. Also, 1.5 degrees can’t do justice to Pleiades. Borderline at best for Beehive. So you miss out on some of the precise targets that one gets an 80mm Apo for because of the narrow AFOV.

1.5 degrees is nice. 3.0 degrees is better.

Scott

But aren’t we talking the capabilities of the OP’s scope ?? Thats what my calcs were based on, why do any other sizes, types of scopes matter ?

[thecelloronin]

Say you have 2* TFOV and have your scope trained on the Andromeda galaxy. You’ll be able to fit most of it in your eyepiece. TFOV is important for framing objects.

 

Now, say you have two eyepieces that both give 2* TFOV, but one has 100* AFOV while the other offers 50*. Both will frame Andromeda the same, but the overall picture will be MUCH bigger in the 100* AFOV eyepiece. It’s like watching the same show on a small and large TV. Same image, different picture.

[LDW47]

Say you have 2* TFOV and have your scope trained on the Andromeda galaxy. You’ll be able to fit most of it in your eyepiece. TFOV is important for framing objects.

 

Now, say you have two eyepieces that both give 2* TFOV, but one has 100* AFOV while the other offers 50*. Both will frame Andromeda the same, but the overall picture will be MUCH bigger in the 100* AFOV eyepiece. It’s like watching the same show on a small and large TV. Same image, different picture.

You are correct but they are asking about zooms not stand alone eps ie ‘ want a zoom ‘ ! Read their OP they state they know the capabilities, their narrow FOV !

[LDW47]

Lets give the OP as much info as possible so they can decide, maybe, on a suitable zoom !

[areyoukiddingme]

With a 650mm focal length, and 5", I think going to about 3mm is likely to be close to as high as you'll want to go most of the time.

 

The simplest solution is one good zoom, a good barlow, and one low power-wide field finder.

 

Something like a 30mm APM ultra flat, and either a Baader zoom with barlow, or perhaps wait for the new APM zoom to show up (but I wouldn't hold my breath, as these things can get delayed).

 

I don't think you'll have a huge advantage having two zooms. I think 50 degrees is about as low in apparent field as I would want to go with most of the time. The Nagler zoom is excellent, but it's a lot of outlay for something that could be replaced with a barlowed Baader.

[SeattleScott]

But aren’t we talking the capabilities of the OP’s scope ?? Thats what my calcs were based on, why do any other sizes, types of scopes matter ?

Ok gotcha so yeah they are topping out at about 1.5 degrees, which isn’t very much for a short FL scope. The 20-40mm zoom they seek doesn’t exist, so a fixed eyepiece is required to do justice to the wide field capabilities of the scope.

Scott

[LDW47]

Ok gotcha so yeah they are topping out at about 1.5 degrees, which isn’t very much for a short FL scope. The 20-40mm zoom they seek doesn’t exist, so a fixed eyepiece is required to do justice to the wide field capabilities of the scope.

Scott

Agree but thats not what they asked and that 10-30 will work well for their needs, regardless !

[LDW47]

With a 650mm focal length, and 5", I think going to about 3mm is likely to be close to as high as you'll want to go most of the time.

 

The simplest solution is one good zoom, a good barlow, and one low power-wide field finder.

 

Something like a 30mm APM ultra flat, and either a Baader zoom with barlow, or perhaps wait for the new APM zoom to show up (but I wouldn't hold my breath, as these things can get delayed).

 

I don't think you'll have a huge advantage having two zooms. I think 50 degrees is about as low in apparent field as I would want to go with most of the time. The Nagler zoom is excellent, but it's a lot of outlay for something that could be replaced with a barlowed Baader.

Give them the price of the Baader with very little if anything to gain, don’t hold back, let it all hang out !

[Jon Isaacs]

But is the TFOV not the one that counts, what your eye actually sees ? What am I missing ?

 

A 32 mm Plossl in the 130 mm F/5 provides a 2.4 degree TFOV at 20x. By comparison, 22x with a 1.5 degree field of view is narrow.

 

The Celestron 8mm -24 mm zoom provides a 1.48 degree field.. 

 

Jon

[LDW47]

A 32 mm Plossl in the 130 mm F/5 provides a 2.4 degree TFOV at 20x. By comparison, 22x with a 1.5 degree field of view is narrow.

 

The Celestron 8mm -24 mm zoom provides a 1.48 degree field.. 

 

Jon

So what is your point ? The OP is talking zooms if I am not mistaken not a 32mm stand alone ep ? Please read the OP, happens every time !

Edited by LDW47, 08 April 2021 - 08:17 PM.

[LDW47]

And the real bonus is that the Svbony 10-30 is so close to parfocal that you won’t notice the difference with a minute tweak of the focuser, if at all !

[SeattleScott]

So what is your point ? The OP is talking zooms if I am not mistaken not a 32mm stand alone ep ? Please read the OP, happens every time !

The OP was asking about a low power zoom because they couldn’t find one, so we confirmed that one doesn’t exist and the OP should consider a fixed eyepiece for low power instead. The 10-30 was mentioned because it is the lowest power zoom on the market, but really just to illustrate the superiority of fixed eyepieces at low power.

Scott

Edited by SeattleScott, 08 April 2021 - 08:43 PM.