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Hi. I have a baader  zoom ii and 32mm plossl which i use loads with my c8. Just for visual and 1.25. A WO dialectic diagonal just because it was really cheap second hand and a Barlow which I never use because the magnification is high enough with a focal length of 2000mm.

Is there anything I'm missing that might be really useful? I'm thinking about the 6.3 reducer and or a 40mm plossl, but I'm not really sure if I'm going to feel the benefit or not.

Advice welcome please. It's so easy to own seldom used kit in this hobby.

Thanks

TimB

 

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Given that the true field of view will be the same with the 32 and 40mm plossls the only reason to get the 40 would be if you feel that there are objects (i.e. nebulae) that would be better viewed with a brighter image (bigger exit pupil) than the 32mm provides. Otherwise, if you are happy with the quality and apparent field of view of your current eyepieces there isn't much need to add any more. 

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Hi. Thanks Ricochet. Are any other types of eyepieces that give a substantially wider field of view or is this limited by focal length of the OTA at F10/2000mm. Would the 6.3 reducer help with this? Lots of physics to learn yet......:happy9:

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The reducer would give a wider true field when used with the 32mm plossl. Other than that, you would need to move to 2" eyepieces to get a wider field of view. The thing is that a C8 is just not a wide field scope. Around a 1.25 degree true field is about as much as you can get with an 8" SCT whatever route you go down.

You current eyepieces are probably covering all the bases that a C8 can cover.

Edited by John

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I have a C8 and a lot of trimmings which include the 6.3 reducer . Honestly I never use the reducer much except when imaging nebulaes like M42 but it will cause some vignetting . But others do use it for viewing and rave how it makes dimmer objects brighter which it does but not too good with planets cause it makes them too bright . It's not a bad thing to have if you have the extra money to spend .

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How can the reducer make objects brighter ?

If anything I'd have thought the additional glass elements plus the lower magnification would have had the opposite effect slightly ?

I can understand that it might produced brighter images when imaging because the optical system is faster, but not for visual observing ?

Edited by John

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Thanks all. Does adding a 6.3 reducer that reduces the focal length also reduce the magnification of the eyepiece used. I'd like the idea of lower magnification and wider field. I know to get really low I need a different OTA.

Thanks

Edited by TimB

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Yes, the focal reducer reduces the effective focal length from around 2000mm to around 1260mm.

Edited by Ant
Thanks John
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13 minutes ago, John said:

How can the reducer make objects brighter ?

If anything I'd have thought the additional glass elements plus the lower magnification would have had the opposite effect slightly ?

I can understand that it might produced brighter images when imaging because the optical system is faster, but not for visual observing ?

Read this , it will explain much better . But a FR changes a f/10 scope to a f/6.3 . That means it makes it a faster imaging scope which makes objects brighter .

https://www.astronomics.com/focal-reducer-field-flattener-combos_c269.aspx

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All explained now thank you.

Sorry for improper use of forum and poor implied language earlier if you read it before it was edited on my behalf. I'm going to  go sit in my shed for a bit now. ASQ34.......

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26 minutes ago, celestron8g8 said:

Read this , it will explain much better . But a FR changes a f/10 scope to a f/6.3 . That means it makes it a faster imaging scope which makes objects brighter .

https://www.astronomics.com/focal-reducer-field-flattener-combos_c269.aspx

Thanks Ron. I know that the faster focal length will help with imaging (as I implied in my post) but I don't think it makes objects brighter when viewed visually ?

(or at least the F/6.3 focal reducers that I've used with 5" and 8" SCT's have not had that benefit)

I've assumed that the OP is referring to using the scope visually.

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38 minutes ago, John said:

Thanks Ron. I know that the faster focal length will help with imaging (as I implied in my post) but I don't think it makes objects brighter when viewed visually ?

(or at least the F/6.3 focal reducers that I've used with 5" and 8" SCT's have not had that benefit)

I've assumed that the OP is referring to using the scope visually.

Like I mentioned I don't use it for viewing planets . When I first got my FR I used it to view Jupiter and a moon transit . I couldn't see the shadow on Jupiter but I could barely make out a couple bands . Took the FR off and used my 25mm Plossi and 2x barlow and could easily see the transit so since then that is why I don't use it for planet viewing . But if you'll notice it does make stars more brighter pinpoint with the FR .

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A focal reducer cannot make things brighter, it can only reduce the magnification by making the focal length of the scope shorter. You canna change the laws of physics as they say.

It does also introduces extra elements - putting more optics in the light path doesn't help brightness. Focal reducers also have a restricted aperture which will lead to low power, wide angle eyepieces vignetting.

The only action you can take to go wider with an SCT is to go for a 2" visual back and 2" widefield eyepieces.

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45 minutes ago, Mr Spock said:

A focal reducer cannot make things brighter, it can only reduce the magnification by making the focal length of the scope shorter. You canna change the laws of physics as they say.

It does also introduces extra elements - putting more optics in the light path doesn't help brightness. Focal reducers also have a restricted aperture which will lead to low power, wide angle eyepieces vignetting.

The only action you can take to go wider with an SCT is to go for a 2" visual back and 2" widefield eyepieces.

Visually, some reducer lenses also allow rich field viewing with medium focal length 1.25” eyepieces. For example, the standard 26mm Plössl that comes with most f/10 Schmidt-Cassegrain scopes effectively becomes a 41mm eyepiece with an f/6.3 reducer, with a 149% brighter image and 56% wider field than its normal view. Some vignetting and a deterioration of the image quality at the edge of the field may be visible, however, particularly with wide field eyepieces. Eyepieces longer than 35mm in focal length are not recommended for use with a reducer lens .

 

The above is a copy/paste from https://www.astronomics.com/focal-reducer-field-flattener-combos_c269.aspx . Not trying to cause a problem but this is what I have read on the internet and have experienced with my own FR .

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4 hours ago, TimB said:

Hi. Thanks Ricochet. Are any other types of eyepieces that give a substantially wider field of view or is this limited by focal length of the OTA at F10/2000mm. Would the 6.3 reducer help with this? Lots of physics to learn yet......:happy9:

With your zoom eyepiece you should see that the "circle" that you see is wider at the 8mm setting than the 24mm setting. This is the apparent field of view (aFoV). Each eyepiece design has a set aFoV, your Plossl will be about 50° and your zoom something like 40-60° depending on what setting it is on. If you have a look at eyepieces on the FLO website (or any other Astro retailer) you should see this attribute listed for each eyepiece. As a general rule of thumb the wider the aFoV the more expensive the eyepiece will be. 

The other type of field of view is the true field of view, this is the actual amount of sky you see through the eyepiece. The upper limit to this is determined by the focal length of the telescope and the diameter of the eyepiece field stop (which is limited by the eyepiece nosepiece). When framing objects you can increase the tFoV by switching to an eyepiece with a larger aFoV or to one with a longer focal length. For example, if you were looking at something with the zoom at the 24mm setting and wanted to see more sky, you could either switch to your 32mm 50° Plossl or a 24mm 68° eyepiece, both of which will max out the tFoV available with a 1.25" barrel. 

I am not sure if the focal reducer will allow wider fields of view or if baffles in the telescope prevent it. I will leave it to those who have tried it to advise on this. 

4 hours ago, John said:

How can the reducer make objects brighter ?

The reducer decreases the focal ratio which will result in an increase in exit pupil and therefore brightness. 

 

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19 minutes ago, Ricochet said:

The reducer decreases the focal ratio which will result in an increase in exit pupil and therefore brightness. 

 

Hmmm..... while I understand the effect of the FR I'm still not sure about the actual benefits of this visually on DSO's :icon_scratch:

Found this post by one of the more experienced members of another forum which sheds a little more light (ha ha !) on the topic:

https://www.cloudynights.com/topic/479239-focal-reducers/?p=6260294

Edited by John

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For my 8 inch sct I use a 25mm ,12mm and a 7mm and use a illuminated cross hair at 12.5mm for star alignment..

The 12mm I use the most..the 7mm I've only ever used twice as the seeing conditions were good enough..

Also I use a 6.3 focal reducer for imaging dso and to get the full disc of the moon in..hope it helps somehow..

 

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23 minutes ago, John said:

Hmmm..... while I understand the effect of the FR I'm still not sure about the actual benefits of this visually on DSO's :icon_scratch:

Found this post by one of the more experienced members of another forum which sheds a little more light (ha ha !) on the topic:

https://www.cloudynights.com/topic/479239-focal-reducers/?p=6260294

I can see three very expericenced members on that thread(GlennLeDrew, John Isaacs and Jhayes_Tucson:smiley:

Referring to my own much limited experiences, for observing galaxies, I usually only thinking of getting about magnification to get galaxies in right size (2° to 3°), any magnification don't change the contrast, so Glenn is correct. While for observing larger nebulas, the magnification is not a primary consideration (it's usually already much larger than 3° in very low mag), especially in combination with a narrow band filter (UHC/OIII/H-beta), larger exit pupil does improve the constrast, since these suitable filters do dim the sky glow much more than the nebulas, so the  Johns (Isaacs and Jhanyes-Tucson) are correct too.:smiley:

More practical examples, For OP with current 1.25" EPs, with an OIII filter, 32mm EP with a f6.3 reducer should clearly show the Veil much better than with the reducer. If OP has good dark sky, with an H-beta filter, 32mm with a reducer should give him a fair chance to see HH, and almost no chance without the reducer.

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An 8" scope is an 8" scope. No optical unit you place infront or behind the scope can make the image brighter! Simple physics :wink2:

A focal reducer will reduce magnification; a Barlow will increase magnification. That is all. Use of the word 'brightness' is misleading. Less magnification and larger exit pupil are the result of an apparent shorter focal length.

Example: a 32mm eyepiece with a 2000mm fl scope will produce x63 - the same as a 20mm eyepiece with a focal reducer.

If we are talking about brightness, then yes, a lower magnification will increase background 'brightness' by increasing the size of the exit pupil i.e. the sky background will be less dark. This isn't the same as object brightness and will, in fact, decrease contrast making objects less visible unless less you have completely dark skies.

 

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6.3 reducer and UHC filter on the way via Astrobuysell bargains. Thanks people. 

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Congratulations!:smiley:

Even though UHC is not the best filter for the Vail, I'm looking forward to read your impression of the filter with 32mm on the Veil, wiht and without the f6.3 reducer.

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I find that compressing an extended nebula down to a size such that it fits within the field of view greatly improves detectability.  Otherwise, you're just looking through it, and you can't distinguish it from the background unless you scan across it by swinging the telescope.  As such, I like really low powers in short focal length scopes for observing larger nebula.  With an 8" SCT and 1.25" eyepieces, many more nebula qualify as too large to fit within the FOV.  Thus, a low power 2" eyepiece can aid in observing many nebula IMHO, but YMMV.

10 hours ago, Mr Spock said:

An 8" scope is an 8" scope. No optical unit you place infront or behind the scope can make the image brighter! Simple physics :wink2:

Indeed.  That is why many observers over here like Eddgie on CN have gone almost exclusively to observing with image intensifiers.  Imagine seeing Barnard's Loop with ease in real time.  I was able to see the Lagoon nebula with ease from within a city at a star party last summer using a nebula filtered image intensifier simply held up to the eyepiece of an SCT.

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On 6/13/2017 at 19:10, Louis D said:

 That is why many observers over here like Eddgie on CN have gone almost exclusively to observing with image intensifiers.

We use image intensifiers (live viewing x-ray machines) in the hospital i work at.  They make these for astronomy? 

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1 hour ago, TimB said:

We use image intensifiers (live viewing x-ray machines) in the hospital i work at.  They make these for astronomy? 

They make them for the military for night ops.  They're quite small and light compared to some of the hand grenade sized eyepieces out there.  They're very expensive for the state of the art units ($2500+).  Availability depends on what country you're in.  The US doesn't allow export of theirs.  Amateur astronomers can't take them out of country on observing trips, either.  There are non-US ones, but they tend to lag behind performance wise.

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And green ... no thanks, but I'm sure some will like it !

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