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# Difference between 3mm,4mm and 5mm TV Delites

Eyepieces
27 replies to this topic

### #26 Starman1

Starman1

Vendor (EyepiecesEtc.com)

• Posts: 50,724
• Joined: 23 Jun 2003
• Loc: Los Angeles

Posted 10 June 2021 - 08:43 AM

It might be noted that the increase in magnification that occurs here can be significant.

On 1000mm focal length, a

5mm = 200x

4mm = 250x

3mm = 333x

The increase from a 5mm to a 4mm is 25%, and the increase from a 4mm to a 3mm is 33.3%

Given that the eyepieces will likely yield high powers in the scopes they are used in, the last jump in particular might jump right past the seeing ceiling of the night.

A 3.2mm would have yielded the same % increase from 5 to 4 to 3.2mm, and a a 3.4mm would have yielded the same magnification increase from 5mm to 4mm to 3.4mm.

Now I can see why both a 3.2mm and 3.4mm eyepiece have existed in the last 10 years and where those odd focal lengths came from.

• mrsjeff likes this

### #27 CHASLX200

CHASLX200

ISS

• Posts: 22,837
• Joined: 29 Sep 2007
• Loc: Tampa area Florida

Posted 10 June 2021 - 06:53 PM

It might be noted that the increase in magnification that occurs here can be significant.

On 1000mm focal length, a

5mm = 200x

4mm = 250x

3mm = 333x

The increase from a 5mm to a 4mm is 25%, and the increase from a 4mm to a 3mm is 33.3%

Given that the eyepieces will likely yield high powers in the scopes they are used in, the last jump in particular might jump right past the seeing ceiling of the night.

A 3.2mm would have yielded the same % increase from 5 to 4 to 3.2mm, and a a 3.4mm would have yielded the same magnification increase from 5mm to 4mm to 3.4mm.

Now I can see why both a 3.2mm and 3.4mm eyepiece have existed in the last 10 years and where those odd focal lengths came from.

Like to see more 2mm eyepieces.

### #28 25585

25585

Voyager 1

• Posts: 13,104
• Joined: 29 Aug 2017
• Loc: In a valley, in the SW UK. Dark end of the street.

Posted 11 June 2021 - 06:21 AM

Like to see more 2mm eyepieces.

You might find a Vixen HR 2mm still for sale somewhere.

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