Eyepiece advice...another thread!

[blinky]

OK Folks,

Just put up my 4 & 5mm EP's for sale as they are no good in the F10 SCT. So...... I am looking for some advice on replacement EP's

I am looking for a high powered EP for the 8" F10 SCT -I am thinking about a 12mm one? I have a meade series 4000 9.6 and a Meade series 4000 UWA 15mm EP (Lovely BTW, my fav EP!) and am thinking I need something inbetween?

I am also looking for something in between my 20mm and 32mm - something like a 26mm 2" Wide Angle (I really like wideangle EP's)

Finally I am looking for the lowest power 2" WIde Angle EP I can get - is 50mm the one to o for or am I better getting somthing in the 40mm range?

Budget.... Well nothing too heavy, I dont min buing 2nd hand and ideally dont want to spend more than say £30-35 for a 2nd hand EP - Does that sound feesable?

[steve_bham]

Hi Blinky, i also have a f10 sct what was wrong with your other EP's?

[blinky]

Being 4mm and 5mm meant they have way too much magnification in an F10 scope.

[Andrew*]

Craig,

I reckon an 8-24mm zoom would be a good bet. You don't have to worry about it's optical quality too much becaus it's f/10 and you've got half what you need in one eyepiece - very convenient.

For your low power, if you find a 38mm SW PanaView or 38mm SWA (Adler Optik, Rigel etc.) you will be getting about as big a TFOV possible from the 2" barrel.

EDIT: 40mm SWAN

Andrew

[blinky]

8-24mm zoom eh???? Hmm....... The thing that always puts me off them is the FoV - I like a nice wide view but these tend to (especially at the 24mm end) have quite a small FoV, or I am mistaken?

[Andrew*]

You're right, Craig,

Most have a FOV of around 40-60° FOV, but the Baader has a bit nicer 50-68°.

You could get away with just 3 EPs I reckon - the Baader zoom, a 26mm SWA (perhaps PanaView, Meade QX, Rigel 26mm etc.) and a 38-40mm SWA.

If you wanted a UWA EP, you could try the Moonfish or Skywatcher 30mm UWA.

All these eyepieces come up pretty cheap second hand, except the Baader - haven't seen one of those for ages.

Andrew

[blinky]

I have a 32mm 2" Wide Angle (Meade QXA or something) so my think is a 26mm 2" and a 40-50mm 2" then something like a 10-12mm EP.

Then I would have...

10-12mm

15mm wide angle

20mm WO Clone (cannot remember what model this is a clone of!)

26mm WA 2"

32mm WA 2"

40-50mm WA 2"

I think that makes a pretty decent EP collection. I will be putting a couple more EP's up for sale today - series 4000 6.4mm and 30mm. The 2" Diagonal arrives next week!

[brianb]

IMO for high power you need two EPs - the 12.5mm and 9mm Baader Genuine Orthos. These are so much better than the aforementioned zoom that it's untrue, and the cost is similar. You need two because the seeing is sometimes (often in my experience) good enough to support the 12.5mm but not the 9mm.

At low power, even 40mm is sometimes too much, especially if your sky is fairly bright (natural (moon) or artificial light pollution). The effect of the secondary obstruction giving a dark shadow in the image & making you very uncomfortable is noticeable if the exit pupil is too large. IMO something around 35mm is ideal, then you can probably drop the 26mm UWA as well ....

[blinky]

Brian I have a 9.6mm Series 4000 Plossl that I will keep for the odd exceptiona night!

So you are saying that anything more than a 35mm will start to show the shadow of the secondry? Do you think there will be much diff in view from a 30 to a 36mm EP?

So it now looks like I am looking for a 12.5mm, a 26mm (2" Fitting) and a 36mm (2"Fitting) - I am considering purchasing a revelation 2" 26mm EP as it's only £30 from Telescope House, how does this EP rate?

[John]

So you are saying that anything more than a 35mm will start to show the shadow of the secondry? Do you think there will be much diff in view from a 30 to a 36mm EP?

I used to have a 38mm SWA eyepiece (a clone of the Rigel ones) which I used briefly with a fork mounted Celestron C8 SCT. I recall that I could see the secondary shadow when using that one so I got a 32mm SWA instead. I also found the combination of a 2" diagonal and the 38mm EP upset the balance of the scope.

The best low power, wide field eyepiece I used with my SCT was a KK Widescan III 30mm which is a 2" EP which gives an 84 degree FoV (more than a Nagler !). Essentially the Moonfish 30mm 80 degree and similar EP's are clones of these - I think I would consider one of these rather than a longer FL EP.

John

[Andrew*]

But even with a 50mm, you only get a 5mm exit pupil in the SCT. Craig's site is quite dark so there's no exit pupil restriction. EDIT: others seem to disagree - interesting! I've never used an SCT, so my understanding of exit pupil theory is probably irrelevant when it comes to the larger COs of SCTs... Sorry

Craig, if you want to have a 70° FOV for your lowest power EP, your upper limit is 40mm in a 2" barrel. You can get up to 56mm but then you will only have a ~50° FOV.

Of course, it's true htat the orthos will provide better views than the zoom. It's about whether you want more FOV, comfort and convenience or more contrast and sharpness.

ANdrew

[blinky]

Something else to throw in the mix...... I have a 2" 2X ED Barlow, if I got a 6mm EP I could barlow that to 13mm and would not need to buy a high power one???

[Andrew*]

Something else to throw in the mix...... I have a 2" 2X ED Barlow, if I got a 6mm EP I could barlow that to 13mm

26mm??? That's a good idea!

[blinky]

Yeah 26mm sorry

I used to have a revelation 26mm EP - thinking of buying another! Then in 2" I would have 13mm 15mm 26mm and 30mm AND...... If I bought a 40mm that would give 20mm (in between the 15mm and 26mm)

[brianb]

But even with a 50mm, you only get a 5mm exit pupil in the SCT. Craig's site is quite dark so there's no exit pupil restriction. EDIT: others seem to disagree - interesting! I've never used an SCT

Yup. A 40mm is fine for DSOs when the sky is dark. If you use it to look at the Moon or a planet (perhaps to check on Jupiter's moons) your pupil will contract to 2-3mm and the central obstruction will be a substantial portion of that. The effect of the CO at low power depends critically on getting the eye exactly the right distance from the eye lens ... some EPs make this easier than others. Also the size of your pupil & its reaction to bright light may differ from mine. I'm just saying that, when there is a full moon in the sky, I find my 40mm EP useless even for star fields containing no bright objects ... it's just too uncomfortable to use.

Put in the mix, Antares W70 34mm 2" ... at £70 this is good value & works well with a f/10 SCT, no it's not up to Nagler/Pentax XW class but OTOH it's a lot cheaper and is IMO about right for low power with an 8" f/10 SCT, where the fully illuminated field is restricted by the size of the secondary mirror & baffle tube. If your SCT is 11", like mine, and you have the large (3.25") SCT thread to 2" adapter, you can benefit from a 40mm wide field EP when the sky is dark.

[Andrew*]

Thanks for clarifying that brian

[blinky]

I have a meade series 4000 QX Wide angle 30mm EP at the moment, I was wondering if I could utilise an even lower powered EP in the SCT. I am thinking about getting the 36mm QX EP now..

[John]

I have a meade series 4000 QX Wide angle 30mm EP at the moment, I was wondering if I could utilise an even lower powered EP in the SCT. I am thinking about getting the 36mm QX EP now..

TBH I think the Meade QX's are a bit overpriced - the 36mm is £76 new from Telescope House wheras the Rigel Superwide 38mm is £58 from Ian King - I believe they very similar designs.

This Cloudynights review between the Burgess SWA's (essentially the same as the Rigel SWA's) and the Meade QX range is interesting:

http://www.cloudynights.com/documents/BurgessSWA.pdf

I think my conclusion would be "why pay more for the QX ?" but yours may be different.

John

[blinky]

Thanks for that John, I like the QX as it does feel nice but if the Rigel is essentially the same and is cheaper then why not eh?

So I think I will get the Rigel 26mm but am still undecided on a 36/38/40 or 50mm EP???

[blinky]

BTW I could not find them on Telescope House's site have you got a link?

Woops just reread your post! It is on Ian King's site!

[blinky]

What about this:

Adler Adler Optik Skarp 38mm 2" fit 5 element SWA Eyepiece

As my low power eyepiece? 70 degree FoV @ 38mm

Or this?

http://www.pulsar-optical.co.uk/prod/eyepieces/rigel/2inchswa.html

[John]

These are the same as the Rigel variants I think, unless anyone else knows better ???

If you order from SnS or Pulsar (same company) do check stock situation by phone 1st !.

Regards,

John

[blinky]

So you reckon they are both the same then John?

[blinky]

Jings!!! This is not as easy as I thought!!!

On looking at Starry Night and adding in the EP's (or a diffrent EP with the same Focal Length and FoV) I can see there is not a lot of difference between the 26mm, 30mm and 38mm.

So..... I am now thinking of getting a 50mm 70degree EP and also a decent high power 12mm ep - specifically for planetry, som something like an Ortho.

Does that make sense? This is the most thought I have put into ep selection and is probablly why my current collection is a bit of a shambles!

So I would end up with (hopefully)

12mm Ortho (Still to buy)

15mm 1.25 UW (I already have)

20mm 1.25 WO Swan clone (already own)

30mm 2" Meade QX Wide angle (Already own)

and a 50mm 2" Wide Angle (Still to buy)

I also have a 2" 2X Barlow so could potentially do away with the 15mm 1.25 in favour of a 30mm2" barlowed but will check that out next time I am out and decide then! But the barlow in the 50mm would also give a 25mm EP from the 50mm one.

Man this is confusing:confused::confused:

[blinky]

In saying that I dont think I can afford a 50mm Wide Angle EP!