Are the lenses you are using different focal lengths between the two enlargers?
Yes, if the negative stage is further away from the baseboard, the exposure times will be longer as light falls off rapidly (1 over the square of the distance).
However, if you are using the same lens (same focal length), the distance should be close to the same between enlargers for making the same size print. Are you sure you have the condensers adjusted correctly for the format you are using in the Beseler 45? This can make a significant difference in where the enlarger head has to be positioned in order to focus the film on the easel.
Also, you need to make sure the developer dilution and temperature are correct. If you have changed developer dilution, or the developer is cold (65F or lower), this can greatly affect how the developer acts. Both can cause longer exposure times to compensate for more dilute developer or colder developer.
As to some of the other comments:
“A diffusion type enlarger uses the inside of the lamphouse as a reflector.”
Not necessarily. Cold light heads such as those made by Aristo have no lamphouse per se, but a series of tubes that form a grid above the film stage.
“However, it usually needs heat absorbing diffusion glass between the bulb and the negative to prevent overheating the negative.”
“If you were to use a large hot bulb too close to the negative, you may experience curling and/or cause permanent damage to the negative.”
Not true with a cold light head or a Beseler/Minolta 45A type color head. Heat can be a problem with standard COLOR heads using tungsten – halogen lamps with mixing chambers (the type in general use most enlarger manufacturers).
But, heat is usually not a problem with condenser enlargers. Also, a piece of “diffusion glass” (opal glass?) would only increase the problem as it would scatter the light requiring even longer exposure times. Heat absorbing glass is usually clear, with a dichroic coating on one side to REFLECT the infrared (IR) back into the lamp house.
By definition (and especially with the Beseler 45 type enlargers) the lamp is separated from the film stage by the condensers in a condenser enlarger. The condensers absorb a great deal of energy in the 12 micron and above wavelength band (heat) because they are large, thick pieces of glass and glass in and of itself is a very good absorber of IR energy. This is why infrared video cameras must have lenses that are made from exotic materials like gallium arsenide, etc. as a glass lens will not pass enough IR energy to the sensor for it to operate.
Secondly, the lamp in the Beseler is further isolated from the film stage by the upper bellows that do not absorb or transmit heat. I have never had a heat problem with my D2V with the metal condenser section that sits directly on the film carrier using a 150 Watt enlarger bulb and long exposure times making 16x20 prints from 35mm.
From my experience with the Beseler 45 enlargers, with a 50mm lens it would not be unusual to have a 30 second or greater exposure time at f/8 making an 8x10 print. This is using Dektol diluted 2:1 with a 3 minute development time and making sure the developer is at 70F.