9 replies to this topic

[caveman044]

I bought an explore scientific first light 8 inch dobsonian, it comes with a "1.25 inch x 25mm SPL eyepiece". I'm shopping around for eyepieces, and I would like to know more about the one that came with my telescope for comparison. Can anyone tell me who makes it, or do you have any thoughts on how it compares to other eyepieces of the same size? I'm sure it's just a cheapo eyepiece and pretty much anything else would be an upgrade.

[maniack]

It sounds like a standard 25mm Plossl. It should be fine, but you'll need more eyepieces to cover a range of magnifications.

[DeepSky Di]

Topic moving to eyepieces forum. 

[EsaT]

PL = Plössl

S stands for marketing BS bingo word super.

 

 

Anyway 25mm Plössl is never good fit for full size Dobson:

Magnification is low, but narrow A(pparent) FOV of Plössl makes achieved/T(rue) FOV narrow and not good for wide low magnification objects. While magnification is entirely lacking for non-wide objects.

~1200mm focal length telescope really needs 2" barrel eyepiece to give wide view to properly fit in Pleiades.

 

For entry level GSO 30mm SuperView would  give ~60% wider view than 25mm Plössl.

SVbony 26mm SWA could be cheaper little narrower alternative.

 

High quality level again costs ~$200.

[jrmacl]

I bought an explore scientific first light 8 inch dobsonian, it comes with a "1.25 inch x 25mm SPL eyepiece". I'm shopping around for eyepieces, and I would like to know more about the one that came with my telescope for comparison. Can anyone tell me who makes it, or do you have any thoughts on how it compares to other eyepieces of the same size? I'm sure it's just a cheapo eyepiece and pretty much anything else would be an upgrade.

The 25mm SPL supposed to be exact same eyepiece as the Vixen 25mm NPL which from what I've heard is a good quality Plossl. I wouldn't replace that as your first purchase. Use that one for now buy another focal length. I think the Svbony SV135 7mm-21mm Zoom would be a good place to start for about $40 or $50. Pair that with a $15 Barlow and explore which focal lengths in the zoom you like and buy that.

[maniack]

The 25mm SPL supposed to be exact same eyepiece as the Vixen 25mm NPL which from what I've heard is a good quality Plossl. I wouldn't replace that as your first purchase. Use that one for now buy another focal length. I think the Svbony SV135 7mm-21mm Zoom would be a good place to start for about $40 or $50. Pair that with a $15 Barlow and explore which focal lengths in the zoom you like and buy that.

If the OP is in the US I'd prefer this 8-24mm zoom over the Svbony. I have both and the 8-24 gets a lot more use.

[dmgriff]

I bought an explore scientific first light 8 inch dobsonian, it comes with a "1.25 inch x 25mm SPL eyepiece". I'm shopping around for eyepieces, and I would like to know more about the one that came with my telescope for comparison. Can anyone tell me who makes it, or do you have any thoughts on how it compares to other eyepieces of the same size? I'm sure it's just a cheapo eyepiece and pretty much anything else would be an upgrade.

It is a basic inexpensive plossl. It works well at the f/6 focal ratio of the ES FirstLight. Plossls and Orthoscopics can be very nice eyepieces. Plossls do have a 50 degree afov (apparent field of view) and orthos are even narrower. I have Televue plossls and Takahashi Abbe orthos that are very sharp in a f/6 newtonian. They do come at a price. I also have some Vixen NPL plossls that are very good also. The Svbony SV207 SuperPlossls are the same optics as the Vixen NPLs at less price.

 

Many have a 32mm or 30mm 50 degree apparent field of view 1.25in Plossl (largest true field of view for a 1.25in ep) as a low power ep. A 24mm or 25mm 65 afov 1.25in ep will give you about the same true field as the 30mm/50afov plossl with slightly more magnification.

 

If you want a 60/65/68 afov 1.25in ep the inexpensive Orion Expanse clones (such as the Svbony Ultra Wide Angle 68 degree series) are good at your f/6 focal ratio, but, will have some edge aberrations I believe. The Astronomics (CNs sponser) has AT PFF series 65 degree afov eps at 40usd and also AT Paradigm Dual ED 60 afov eyepieces (well recommended on CN) and are priced at 70usd. A Svbony SV190 18mm UFF 65 afov (clean to the edge) is still 90usd (24mm UFFs and other 18mm are ~150usd+).

 

Alot of CNers like 82 afov eyepieces with a manual push dob. Astronomics has a line of those at ~100usd.

 

Many will recommend a inexpensive zoom to start with. Be aware that they will have narrow fields of view at the lower powers. The afov increases as the focal length decreases. 

 

I had a ES FirstLight 203/1218 dob out last night to view the very bright Moon. I used a 80A Blue Wratten filter to mitigate the glaring brightness and improve contrast with 24mm, 18mm UFFs, 13.4, 9.4, 4.9mm Speers Waler 82afov, Orion EdgeOn 6mm 55afov. Also, a "set" of a 30mm/50afov SV207 plossl and Tak Abbe orthos 18, 12.5, 9, 6mm ~44 degree afov. The Tak Abbes were the sharpest to my eyes. I also got out my Binoviewers with Astronomics ATPF 25, 19mm eps with a AT2XTB telecentric 2x barlow to reach focus. The 25mm (working at 12.5mm with the telecentric barlow as optical corrector to reach focus) framed the full moon nicely. The 2.5in Hexafoc r&p focuser handles a binoviewer easily. The optical tube of the dob is steel so some magnets at the back end will balance anything heavy. My tube is set pretty near the base and even with the large trunnions a hefty StellaLyra 1.25in 24mm UFF is a little nose heavy). You will find some kind of observing chair useful.

Edited by dmgriff, 12 April 2025 - 05:45 PM.

[Tony Flanders]

25mm Plössl is never good fit for full size Dobson.

I disagree. Every telescope needs a workhorse low-power eyepiece, and a 25-mm Plossl does that job just fine for an 8-inch f/6 Dob. In the fullness of time you will likely want to switch to an eyepiece that gives a wider true field of view -- perhaps a 32-mm Plossl, a 24-mm widefield, or a 2-inch eyepiece of some kind. But meanwhile, the 25-mm Plossl provides a field of view wide enough to fit all but the very biggest deep-sky objects, and also for reasonably convenient star-hopping.

I concur with the consensus in this thread that the next place to concentrate is on higher magnifications.

[PalomarJack]

I bought an explore scientific first light 8 inch dobsonian, it comes with a "1.25 inch x 25mm SPL eyepiece". I'm shopping around for eyepieces, and I would like to know more about the one that came with my telescope for comparison. Can anyone tell me who makes it, or do you have any thoughts on how it compares to other eyepieces of the same size? I'm sure it's just a cheapo eyepiece and pretty much anything else would be an upgrade.

Here's my point of view, "For every doubling of power you will use that eyepiece/magnification half as much".

 

To find the ideal low power, multiply your aperture in inches by 4. That is known as 4X per inch. Divide the focal length in millimeters by that result and this gives you the focal length in millimeters of the eyepiece.

 

Now, smaller aperture longer focal length telescopes become unwieldy in the eyepiece department, so you have to use "best practice". Like my 127mmx1200 refractor at 20X would need a 60mm eyepiece for lowest magnification. This is where Best Practice comes in. It's nicer term for common sense. Now, for a fast f/ratio it works much better. My 12" f/5 gets a 31mm, 48x for about 4X per inch.

 

From here, the next would double the magnification, and the next, double again. On up to no more than about 50X per inch. But here, Best Practice takes affect again. A 16" at 50x per inch is just nuts. That's 800x, very rare the atmosphere will even support it. So, in this case, stop at about 400x. Besides, at 800x even a 100* eyepiece will only yield 7.5 minutes, .125 degree, or, 1/8 of a degree FOV. Not very much and will only get you seconds of viewing.

 

Hope this helps, and clear skies to you.

[Starman1]

Here's my point of view, "For every doubling of power you will use that eyepiece/magnification half as much".

 

To find the ideal low power, multiply your aperture in inches by 4. That is known as 4X per inch. Divide the focal length in millimeters by that result and this gives you the focal length in millimeters of the eyepiece.

 

Now, smaller aperture longer focal length telescopes become unwieldy in the eyepiece department, so you have to use "best practice". Like my 127mmx1200 refractor at 20X would need a 60mm eyepiece for lowest magnification. This is where Best Practice comes in. It's nicer term for common sense. Now, for a fast f/ratio it works much better. My 12" f/5 gets a 31mm, 48x for about 4X per inch.

 

From here, the next would double the magnification, and the next, double again. On up to no more than about 50X per inch. But here, Best Practice takes affect again. A 16" at 50x per inch is just nuts. That's 800x, very rare the atmosphere will even support it. So, in this case, stop at about 400x. Besides, at 800x even a 100* eyepiece will only yield 7.5 minutes, .125 degree, or, 1/8 of a degree FOV. Not very much and will only get you seconds of viewing.

 

Hope this helps, and clear skies to you.

It depends on what exit pupils work for you, how bright your skies are, and what objects you observe.

 

My eyepieces range from 60x to 500x, and the most used are in the 130-200x range.  I use 60x in my 12.5" about once a year, and usually with a filter on larger nebulae.

Your rule doesn't work for every type of observing.

For planetaries, I'm often in the 300-500x range.  For galaxies, in the 150-250x range.

 

In brighter skies, 4x/inch is a very washed out image.  Heck, 7x/inch is a washed out image.  Even at a dark site, I often start my observing above 10x/inch.

 

Your 4x/inch is an exit pupil of 6.35mm, an exit pupil size few observers older than 50 can use.

5x/inch is more practical (5.1mm exit pupil) or even 5.5x/inch (4.6mm exit pupil) for older observers.