Baader D-ERF Question

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marktownley
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Baader D-ERF Question

Post by marktownley »

May sound a daft question this, but will ask anyway...

The Baader 110mm D-ERF, is the total diameter 110mm - ie basically 100m when mounted in a cell, or is its clear diameter 110mm so it's total diameter larger than 110mm?

Thanks in advance...

Mark


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Re: Baader D-ERF Question

Post by Bob Yoesle »

Hi Mark,

The bare DERF 110 filter is 110 mm x 8 mm.

The clear aperture on the cell TS made for me is 102 mm:




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Re: Baader D-ERF Question

Post by Merlin66 »

Yes.
I have the 90mm version and managed to squeeze a clear 88mm out of it....


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Re: Baader D-ERF Question

Post by marktownley »

Yes.
I have the 90mm version and managed to squeeze a clear 88mm out of it....

Thanks everybody! Yes I intend squeezing as a much as possible out of the 110mm ;)


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Re: Baader D-ERF Question

Post by MapleRidge »

Hi all...

A further question on the ERF's. Can you use the same ERF material and mounmt it inside if the OTA behind the objective to permit a smaller diameter piece of glass? If so, how far in can you effectively do this. Could you use a 75mm OD ERF behind a 100mm objective? I realize that the spacing would depend on the lighyt cone (f ratio) but I would expect that if you intercept the light cone too far along the path you would have too much sunlight concentrated on it.

Just wondering aloud :)

Brian


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Photos: https://www.flickr.com/photos/185395281@N08/albums

10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
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Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
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Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
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Re: Baader D-ERF Question

Post by Merlin66 »

Brian,
The general answer is yes. Some amateurs (Peter etc) are already using this arrangement.
I looked at it for the LASS and LADS configuration.
The ERF reflects 99%+ the input energy so care has to be taken with it's position relative to the focus; you don't want to end up re-focusing 99% of the energy back onto a small spot on the back your objective!!! I suggested the ERF should be larger than 50% the aperture and positioned <50% the focal length from the objective. Some consideration should be given for removing the heat load from the interior of the OTA.


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Re: Baader D-ERF Question

Post by marktownley »

Can you use the same ERF material and mounmt it inside if the OTA behind the objective to permit a smaller diameter piece of glass?

Yes! I'm sure others will answer in more detail on the last part of your question...


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Re: Baader D-ERF Question

Post by peter drew »

Today at full aperture I was using 220mm, 150mm and 100mm PST modded scopes with 140mm, 105mm and 75mm internal ERF's respectively with no problems. :)


colinsk

Re: Baader D-ERF Question

Post by colinsk »

The limit is going to be temperature related. If you overheat the ERF and it cracks you have it too far back in the tube. If this happens use a larger ERF higher in the tube and view with remaining eye. ;)


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Re: Baader D-ERF Question

Post by MapleRidge »

Thanks everyone for the info passed along on the internal ERF question. I have a mod in mind, just trying to sort out the details.

Brian


Brian Colville

Maple Ridge Observatory
Cambray, ON Canada

Photos: https://www.flickr.com/photos/185395281@N08/albums

10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
C14 + Lunt 80ED
Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
Planetary Work - SBIG CFW10, ASI462MM

2.2m Diameter Dome
iOptron CEM70G Mount carrying:
Orion EON 130ED, f7 OTA for Day & Night Use
Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
ASI1600MM, ASI432MM, ASI294MM Pro, ASI174MM, ASI462MM
peter drew

Re: Baader D-ERF Question

Post by peter drew »

No heating problems noticed so far with subdiameter ERF's provided they are placed less than halfway down the light path. The Baader ERF's seem to be the best, reflecting pretty much all of the heat back out through the objective. :)


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Re: Baader D-ERF Question

Post by MapleRidge »

Thanks Peter...
This is all new tome (doing the mods), so I was wondering if it were necessary to vent the tube between the objective and erf, or if an internal mount needed different specs to be successful.

Thanks to everyone who chimed in...much appreciated.

Brian


Brian Colville

Maple Ridge Observatory
Cambray, ON Canada

Photos: https://www.flickr.com/photos/185395281@N08/albums

10'x15 Roll-off Roof Observatory
Takahashi EM400 Mount carrying:
C14 + Lunt 80ED
Deep Sky Work - ASI294MM Pro+EFW 7x36/Canon 60D (Ha mod), ONAG
Planetary Work - SBIG CFW10, ASI462MM

2.2m Diameter Dome
iOptron CEM70G Mount carrying:
Orion EON 130ED, f7 OTA for Day & Night Use
Ha Setup: Lunt LS80PT/LS75FHa/B1200Ha + Home Brew Lunt Double Stack/B1800Ha on the Orion OTA + Daystar Quantum
WL, G-Band & CaK Setup: Lunt Wedge & Lunt B1800CaK, Baader K-Line and Altair 2nm G-Band filter
ASI1600MM, ASI432MM, ASI294MM Pro, ASI174MM, ASI462MM
peter drew

Re: Baader D-ERF Question

Post by peter drew »

Side by side by side comparisons with external and internal ERF's have so far shown no difference in image stability due to heating when used visually, any disturbances appeared to be ambient seeing issues. My 150mm F10 has a full length 180mm od main tube.


Roel

Re: Baader D-ERF Question

Post by Roel »

you don't want to end up re-focusing 99% of the energy back onto a small spot on the back your objective!!!
Why is that? The vast majority of the energy will just pass right through the objective, so the heat won't be absorbed by the objective and cause problems? I mean, it all got through it on the way inside.


peter drew

Re: Baader D-ERF Question

Post by peter drew »

There is no significant heat untill close to the focus, remember as kids when we used magnifying glasses to burn holes in paper, you had to get it focused. The returning beam reflected from the ERF comes to a focus and produces enough heat to char wood, best to keep this forward of the objective! :)


Roel

Re: Baader D-ERF Question

Post by Roel »

The returning beam reflected from the ERF comes to a focus and produces enough heat to char wood
Of course, but that's because the wood absorbs the energy of the focused beam. Glass lets it through. A Hershell prism for example is very close to focus, but doesn't catch fire!


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